Those of us that have attended competitions before will attest that there are certain things that are invaluable on those days.
Most serious competition archers have a tent. This can be anything from a golfing or fishing umbrella to a gazebo or 4-person family tent. Protecting yourself and your equipment between ends is good practice.
A comfortable Camping Chair. When you are not shooting arrows then you will probably be using this. During your days at a competition there are various breaks, lunches, target moves, stoppages, collecting a lot of arrows and waiting for results so having somewhere to sit is useful.
A Big bottle of water. Fields are not known for having the best access to drinking facilities so bringing your own water will make it easier. On a hot day you will be drinking a lot so make sure you know where the toilets are too.
A Shooting Hat. This can be a baseball cap, beanie, bucket hall, trilby, Stetson, etc…. Whatever feels comfortable to shoot in. Sometimes it can be windy, wet, or both, hot, dry, dusty or all of the above. Wearing a hat protects your head, your eyes from the sun, stops any sunburns and if the day is hot then dipping your hat in a bucket of water is quite refreshing.
Sun cream. No matter what the weather looks like it is easy to burn in the sun. Competitions are in the middle of open fields, with no shelter or tree’s, so for 6 + hours you will get the sun’s rays directly. Load up on your factor 30 at every break and make sure you have something to wipe your hands on.
Toolbox. During your time shooting you will have fletching’s fall off, piles fall out, rests snap, nocking points move and many more exciting events. These things like to happen you are at a competition so amassing a few easy to carry tools that will go everywhere with you is a good plan. Every has a different box with gadgets and gizmos as well as springs, spanners, and Allen keys but there are some essential items.
Allen keys (metric and imperial)
Knife with scissors
Sharpie marker (other brands exist!!)
Arrow and bow spare parts (fletchings, nocks, pressure buttons etc)
Snacks. During a competition, irrespective of the length, you will need to keep your energy levels high. Snacks like nuts, fruits and picky bits will help to do that without too much effort.
Clothing. No blue denim, camouflage, or Dark olive!!! This is an old rule but still stands. Also all tops must cover shoulders (having sleeves) and mid-riffs at full draw. All footwear must be enclosed and all long hair tied back, due to health and safety.
Spotting Scope. When you get to shooting the further distances, it can be hard to spot arrows and correct any mistakes so using a scope after every couple of arrows can save many lost points.
This list is by no means exhaustive, but it gives a good starting point to anyone.