Welcome to the forum!
The woolly bugger is possibly the best all-purpose fly for trout that can be used anywhere in the world. You can fish it like a nymph by dead drifting it or gently twitching it, which can also imitate a dead or injured baitfish. You can fish it like a streamer by stripping it in. Depending on how its tied, the current speed, and how you fish it, you can also fish it as an emerger. Everywhere I've gone, black and olive are the two standard colors. White or yellow are good to have too, plus a couple of sparkle buggers in olive and black. I've had fish ignore repeated casts with a regular black bugger and slurp up the black sparkle bugger on the first cast. Sometimes they like it flashy!
You should also have a couple of streamers in your fly box that imitate the local minnows in the rivers where you're going. Size and shape is more important than color. In general, the same colors that work for woolly buggers work well for streamers too!
How much fly fishing experience do you have?
My passion for catching fish is eclipsed only by the fish's passion not to be caught.