Music helps me a lot when I start losing focus/hype.
Also, eating breaks are key. Tons of people just have a large breakfast at the start of the day of a big tourney and don't eat again until around dinner. This is pretty awful, but it happens for a reason - it's hard to get out sometimes with brackets running, and not wanting to miss out on the opportunity to get more games in. Ignore those temptations. You're an organism. Organisms eat and drink things a lot. Organisms aren't made to sit down in chairs for 8 hours straight. Before an event, plan out when you can take a break between brackets you enter, or plan to go right after you get knocked out of bracket. Look up nearby restaurants. Better yet, pack a lunch! If you can bring a console or CRT, you can most definitely throw in a wrapped sandwich or something. And whether it's a small snack or full lunch you bring is optional, but water bottles should be mandatory. Keeping hydrated is obv just as important, and perks you up more quickly if you're losing focus anyhow.