Players not paying attention during game-
In the past, I never had any issues getting players to maintain focus while gaming. Nowadays, there are so many things that draw players focus away from the game, and I've found too many players that actively do things on computers or other items that keep them focused on something other than the game at hand.
Don't get me wrong... I know that I have been distracted during game from time to time, but I try to make sure I pay attention as much as possible. And every gaming group will go off topic about various subjects. I often joke about talking about The Walking Dead at my weekly Pathfinder game because it's a common topic before we begin. It occasionally has the effect of bringing everyone back to focus on the game with a good laugh.
Players not prepared for game-
When you have a regularly scheduled game, you should know that you need to bring everything you need to it before you leave for the game. Also, I game with players that have been doing this for several years. You shouldn't have forgotten key materials like your dice or your character sheet. I can understand forgetting to bring your characters mini from time to time, and that's why I now always have mine in my backpack all the time.
You don't have to be a boy scout to be ready for game.
Food for players-
In many of the gaming groups I have been apart of, we have usually made plans ahead of time for meals or snacking during the game. Occasionally... when the location of the game happens to be at someones house... there has been the expectation of the host providing said food.
A past Pathfinder game I was part of had a tradition of doing a potluck every 2nd Sunday of the month. I really like this idea as it doesn't put a heavy weight load on anyone. It's worked very well. My issue is when offering food for the game... such as when it is held at your house/apartment... become an expectation from the visiting players.
It's one thing to offer a meal on occasion while game it at your place, but it's another when the players expect there to be food for their consumption when they visit. This has been a problem in the past when I have helped to host games at my home and this has been the downfall of a couple of gaming groups I have been in.
Kids at game-
I understand that some parents are not able to get childcare all the time, but there have been so many times where the game has been hampered by children who have been brought to game.
Your scheduled game time is not a time where you should bring your kids all the time. In many of the games I have participated in, the themes run from casually adult related (i.e. The occasional "foul" word) to downright R-rated (i.e. Foul language and dramatic scenes of violence and death).
While some parents don't care if their children are bombarded by such things, that isn't the full extent of my issue with kids at game. I started gaming at age 10, and was well versed in the 4-lettered words as well as graphic violence. My biggest issue is the fact that your scheduled gaming session is not daycare.
Children get bored and will accost either the parents or other adults in the gaming group to either get some kind of attention or try to find something to do that will occupy their attention for a while longer. This becomes a larger issue when the parents of these children do nothing to control them.
In addition to those parents that bring their children to game and leave them to their own devices without actually working to parent them because game time is their time, I'm upset at those parents who think that they can just sit their children in front of a TV (with either video games, movies or shows) and think that everything's going to be fine... especially with multiple children that may have attention disorders. Kids get bored of watching the same show, and multiple kids won't often agree with playing the same video game for an extended period or watching the same movie. This has been a contributing factor to the downfall of gaming groups that I have been a part of.
Life happens. We all know this. There are problems that you should concern yourself with, and there are those that you really shouldn't. Don't bring your dirty laundry to your game and realize the difference between a real problem and what is generally called a "First World Problem".
If you have real problems that others in your gaming group may be able to help you with, then sure, bring them up for discussion to help you better resolve whatever situation is going on in your life. traditionally, gaming groups are formed from people who are friends, and as a friend they should have a vested interest in helping you when they can. However, you shouldn't make the entire gaming session about resolving your issues. You're there to game and have some fun. A time to step away from the vicissitudes of the real world to partake in some fantasy time.
If you're overly concerned because another game you attend didn't go well for you (or your character), and you allow this to affect your mood that disrupts the current game session, don't bring it to your game session.
As my regular readers and friends know, I was a part of The Camarilla and Mind's Eye Society for many years. One of the reasons I'm no longer with the current organization is the fact that there was too much drama being brought to games as well as through the various out-of-game sources of communication. Because these groups were large organizations, there was a great deal of political drama in and out-of-game.
If you let what happens to you character in-game affect your mood out-of-game, you should really take a look at your priorities, IMHO.
I understand getting attached to your characters over time, but they are only characters on a piece of paper. They do not really bleed. They do not suffer from being unemployed for a long time. They live and die during your game sessions. It is said that there are 2 things you can never avoid: death and taxes. Most games don't deal with taxes but just about every game deals with death.
I come to game because I want to role play to get away from the vicissitudes of real life. I do this by interacting with other PC's and NPC's in the games environment. My character has a rich and developed background that I worked on before the game began. It was submitted for your review so you could come-up with ways to use it within your game. Why don't you allow me to complete certain tasks setup within my background when it doesn't interfere with the game?
Players using out-of-character information in game-
Sometimes a DM/GM/ST doesn't have the opportunity to take time out of game to convey information that only certain PC's should/would know. Because of this, that information is conveyed to the player during game in front of all the players.
Though this info was directed at a specific PC or group of PC's and not the entire group, some people treat this information as common information and act upon it. This makes having secrets in your characters background and keeping secrets from other PC's very difficult.
During my time in The Camarilla and Mind's Eye Society, this was a large issue the ST's faced because there was little they could do about the fact that they needed to provide information to a small group or individual when they are running a game for a very large group. Thankfully there were only a handful of people who would occasionally use this kind of information improperly.
What really bugged me about my time with The Camarilla and using out of game information in game was when it was utilized by storytellers at a higher level. For instance, there was a PC who had committed diablerie in our vampire game. No PC's were aware, but this detail needed to be on an official ST report to the regional storyteller. Shortly after this information was reported, a group of players (a couple assistant regional storytellers included) came to our game, found the "offending" PC and worked to deal with it in game without any provocation or way they could have known about the diablerie.
Before the inclusion of technology in games, we normally passed written notes for these types of secretive communique's. In the past, I have personally utilized instant messengers that they players have had access to. I know that many places you would normally play have some kind of WiFi access, I also know from personal experience that they are not always very reliable. This is why I would prefer to keep my tabetop games at someones house where the WiFi isn't being used by everyone outside of the game.