Even if you are at full health, once it gets down to the last 15 or so people it is a good idea to start popping those energy drinks and painkillers to get you boosted up and regenerating health. There’s a few reasons for this, such as not having to worry about it after a late game fight, as well as the potential that one tick of health recovery could win you a close battle. Either way, if you have them available you should get the boosts going early as there's no point saving them. Who wants painkillers with a chicken dinner?