Gi (or no-gi attire). Bring a backup gi if it's IBJJF cuz you might DQed. I shouldn't have to say this, but I do.

Water bottle/electrolytes. Gatorade, LiquidIV, whatever you need in terms of hydration.

Snacks. The longer I do this, the less I bring in terms of snacks. Some bananas, honey, and maybe a couple bars is a good enough for me. Maybe some chocolate for afterward :)

Mouth guard. If you don't use a mouthguard, I pray for your jaw and teeth. If you do use one, don't forget it.

Scale. There's not really a good way around this one. Sure, a local gym or hotel might have its own scale, but it might not be accurate. You need a scale you trust before your big event. It goes through security just like a laptop.

Enough clothes (or access to laundry). When you compete you will get sweaty. Don't be the person going home in stinky gear.

Toiletries. Tournaments can be rampant with skin infections. Bring your finest soap and shower as soon as you can.

Headphones. Noise canceling headphones are essential for travel. Nothing ruins an inflight nap like a screaming baby or talkative stranger. Plus headphones are essential for a warm-up.

Book/journal. Domestic travel is a goldmine for thinking and learning. I do some of my most enjoyable reading and writing in transit.