Well a really good idea, if you can, is to take a preliminary trip to the river to see what is hatching/present. If you can't a good selection of flies always includes some generic nymphs, dries and terrestrials - if I remember correctly, grasshoppers are fairly prominent round those parts, yeah?? Take a couple Dave's hoppers with you, they're one of my favorites. Take some dry flies like royal coachmen, standard Adams, parachute Adams, quill Gordons, some caddis patterns. I have had really good luck fishing very small (18-24) serendipity's as my searching pattern, with a red body and bleached hair...very buggy looking, I guess!!
Take lots of flies, and do your research as far as what will be hatching at that time. Also, make sure you have some floatant/sinking agent with you - these often forgotten items are indispensable!! I never leave home without a bottle of each.
Also, welcome to the wonderful world of fly fishing
And say goodbye to the wonderful world of financial prosperity while you're at it