In an upcoming session, my players will be fighting a really powerful dragon, who acts as the "boss monster" of this part of the story. The players already know where he is and more or less what they're up against, so they are capable of planning ahead.
The last time we had a fight anything similar to this, the players did a lot of their planning in terms of strategy and buff selection during the session. For the tactically minded players this is great fun. For the others, they will follow whatever strategy is determined and otherwise not pay attention during that. (I have tried to encourage them to do this in the Facebook group for the campaign before the session, with mixed results. It seems to work better with item shopping/crafting lists than it does with combat preparation.)
Between the planning and the actual fight, this single encounter will likely consume an entire session (sessions are typically 3.5-4 hours, starting at 7:30pm). The last time this happened, I noticed that people were really tired by the end of it. More so than usual. It seems to take a lot out of them, and being tired led to mistakes. Tired mistakes against what they're fighting this time will likely get people killed.
I have no problem with killing players in a fight like this, but I prefer it to not happen simply due to people being worn out and unfocused. Thus, what I'm looking for are some strategies to create an atmosphere that will help keep people awake for the entire encounter.
We play at my house, in the living room. Most players are sitting on a couch with reclining seats, with a couple in chairs pulled up to the area. The game board is a whiteboard on top of the ottoman, and I sit on the floor across from everyone else. The room is pretty bright, and I don't have a practical way to make it any brighter (I can make it darker pretty easily). There isn't typically music or distractions like that.
Snacks are on an "if someone feels like bringing some" basis. Usually it's junk food of some sort (chips, ice cream, cake, donuts, etc). Drinks are typically water and coffee that people bring with them. Typically, people are tired enough to be ready to go home by the end of the session, but still reasonably energetic (ie: they're alert and thinking clearly). For this type of situation, I can get or cook something.
On these really long encounters, people are far more likely to start to nod off or generally act more tired.
I tend to keep combat going fairly quickly, so that players don't wait a long time between turns. Except when someone has to look up a spell or the grapple rules, long turns are usually not a problem. Given the nature of the boss fight, player turns tend to go slower. I am going to study ahead of time so that the NPC turn will not take a long time.
What I have
We're playing at my house, so we have access to my kitchen. That includes stove, oven, fridge, deep fryer, and a gas grill. So, I can prepare almost anything in terms of food. We're also in the city, so ordering things like pizza is easy.
There is a TV and stereo in the room, with cable, Netflix, and a wide variety of music available. I can't crank the stereo up that high due to a sleeping baby upstairs, but I can use it.
The space is big enough that people can get up and walk around, but the area around the game board is pretty tight, so other people have to move to let folks out. That tends to discourage people from walking around a lot, normally. It is possible to open this up more, if I move all my DM books/maps and sit on the same side as the players.
Any suggestions on what I can do/change to help players stay awake?