Since this is under tournament poker I'm assuming OP is talking about tournament play where long breaks can't often be taken and where play style should and does change as the tournament grinds on.
I've recently begun getting back into some tournaments online (due to a month or so of more free time) and there's players here that know a ton more than me on tournament play here...
but I'd say in terms of staying focused: keep hydrated yes. Stretch, get out of your seat and move around. Take full advantage of the 5 minute hourly breaks.
As for play style I'll say the following:
- How you play certain hands based on position not only matter but also in different stages of the tournament: early, mid, late, final table.
- If the tournaments are deep, turbo, rebuys, add ons, double stacks, etc all matter. If I'm in an early stage of a rebuy and am following my own BRM for R&A tournaments, I'm absolutely getting in with good preflop hands like AKo. Mid stages or late stages I might be folding those hands. Why? Because an early chance to stack up is good and I can rebuy with little damage early on. So more risks.
- Obviously your style of play will vary but as the tournament goes on you'll need to adjust so I wouldn't say your style will always stay static in tournaments. As blinds increase, players bust, and the money is closer in sight watch how people tighten up usually and exploit that.
Just my two cents. As for focus during games, make sure you stand up and stretch, stay fed, stay hydrated, and focus!