I’ve written about this before, but the short story is I like using a Two fly box system. The first box is what I would call my warehouse. It’s filled to the brim with hundreds of popular proven flies. If I’m hiking into a spot I’ll transfer all the flies I need out of the warehouse and put them into a smaller fly box.
Unless I’m in my canoe or a drift boat I only bring TWO fly boxes with me. My system details using a BIG fly box like the SUPER DURABLE Cliff Bugger Beast (Link to AMAZON for the reviews there) as a fly warehouse, I’ll bring this with me if I’m fishing out of a boat.

Then when I’m wading I’ll carry two boxes in my SLING PACK one for STREAMERS and DRY FLIES.
The Streamer Fly Box is the inexpensive SALMON FLY BOX (Amazon link – an AMAZING PRICE) What I like about this box is it’s length and height. Plenty of room for streamers without mucking up the tails and wings.
For DRY FLIES I like seeing into the box before picking out the fly. For this I recommend the one of several sizes from MAXCATCH (Link Amazon for reviews and pricing).

I’ve written all over this website about fly boxes. (if you can keep a secret, I actually sell fly boxes like what’s below)

You can read more about selecting and benefits of different fly boxes in my article HERE.