It kinda depends on if you are driving yourself, or riding with someone else. If you're riding along, you need to be a little more minimal. You should be able to fit everything you need into your bag and maybe a small backpack.
1. Dont throw new plastic, or shots that you havent practiced much. Throw what you know. This might be 20 discs or might be only 5.
2. Bring backups for what you know, in case you lose something.
3. Get a fold-up stool or something similar. You will spend a lot of time waiting, and sitting on the ground sucks.
4. Bring lots of water and snacks.
5. If you dont know the area, or dont feel like eating fast food, bring a lunch.
6. Bring extra socks and an extra shirt.
7. Bring suntan lotion, even if it isnt super bright out. You're spending all day outside.
8. If you have a rulebook, bring it.
9. Make sure your discs are marked.
10. Make sure you have at least one mini.
During the round:
1. Dont talk or move around while other people are throwing. This goes for people on other holes also, if you are within earshot or in their line of sight.
2. Watch the lines that other people throw, and use their shots to gauge the wind.
3. Double, triple, quadruple check your score when the round is done. Two stroke penalty if it's wrong!!!
4. MAKE SURE you check the board for what hole you are really supposed to start on. There's always one or two idiots who look at it really quickly and mistake themselves for someone with a similar name. Then you're out at the wrong hole with 2 minutes left before tee-off and they have no idea where they're supposed to be. Its not hard, just look for YOUR name!!
5. if you dont know, ask!! This goes for anything. Rules, course, OB, whatever.
Above all, remember that you're there to have fun! Too many people take it too seriously and spend all day pissed off that they arent making great shots. You probably wont shoot as well as you would casually or in a league. Dont let it stress you out.