I like to make funny faces. It's less effective on the internet.
For a long tournament game it's probably a good idea to relax a bit, though shutting off completely is not such a good idea. If you don't have a ton of stamina to play a 3-day tournament without trouble, deciding when to use your energy becomes a factor just as deciding how much time to take on a move.
In the opening, you are wondering whether they are following the path you have planned. In the end game you are furiously calculating possible combinations. But in the middle game you can't possibly calculate the number of possible responses, so how should you manage your time when it is your opponent's turn? Rest your brain? Snooze for a bit? Concentrate on your plan and how it could most likely be scuppered by your opponent. Try to work out his plan?
For me the overwhelming temptation is to snooze for a bit and rest the brain.
zzzzz
what? checkmate?