Well, figure out what you need for the coldest day, the warmest day, and the wettest day. Then add a few pairs of clean underwear. Presto!
The key is to layer. If I were going on a ten-day drip during the summer, I would start by deciding what I would need when it was warm. That would be a light synthetic T-shirt (Patagonia Capilene 1 T-shirt, $39), and a light pair of shorts (ExOfficio Amphi Shorts, $50).
Temp drops a bit? I put on a warmer layer, like the Icebreaker long-sleeve Atlas Half Zip ($65) for the torso, maybe the Cap 1 tights ($40) for the legs.
Cooler still, add a fleece jacket (Mountain Hardwear Windstopper Tech Fleece, $185), and some pants (Arc'teryx Gamma LT, $169). I might also add a down sweater, such as MontBells Ex Light Down jacket ($160). Thats for here in Washingtonmaybe not so good in humid Minnesota. Add instead a heavier wool layer.
Then, when wet, some rain gear. REIs Shuksan ($299) is fantastic; theyd go well with Marmots PreCip Full Zip Pants ($90), which arent as breathable as the Shuksan jacket but would be fine when sitting in a boatand could double as an extra warm layer.
Then, as I say, add some changes of underwear, and youre off!