Flies are very specific to the fish and the river but generally a few small nymph patterns such as a gray quill emerger, a midge and a pheasant tail work well in most fisheries. A caddis or mayfly or small grasshopper also often are all purpose dry fly patterns that work well in most places. I’m guessing you’d want to stay fairly small for the nymphs like size 14 or maybe even smaller. Not sure about the dries. Typically, a size 14, 12 or 10 are pretty safe to stick with.
When I visit a new place that I have never fished before I like to stop into a local fly shop. They have the intel on flies for their water. I usually buy a few flies they recommend and ask about good fishing spots. Since you’re making a purchase (even a small one) they are more likely to chat it up and share some local information with you. Flies can add up quickly so bring your own but consider buying a few from a fly shop in town and getting the local scoop from the horse’s mouth. Here’s a few of our favorites that seem to work in most places during the majority of the fishing season: