I bought Costco jerky and have put that in some resupply boxes, just because I've got the membership. I've bought trail bars in relative 'bulk' that way as well as their gorp and dried fruit for the same reason. So a couple more thoughts in terms of thru-hiking food items from Costco ...

Trail bars work great that way because it's easy to resize the big box 'o bars down to the individual bar for different resupply boxes. On a long enough trip and/or with enough resupply boxes, you can buy several different types to add some variety. I do recall buying some sort of "protein" bars which had an attractive chocolate coating over a sort of white gooey protein-rich (I think soy) core. I liked them briefly and then came to loathe these, but other bar choices worked out great.

The Jerky comes in, if I recall correctly, 9 oz size containers. If you have a vacuum sealer at home, consider repackaging into the size you want if it's much different from 9 oz, and have your at-home resupply person put the repackaged units in the freezer until time to mail. If not, 9 oz can sometimes be perfect but is often an awkward amount. I don't find Kirkland brand jerky to be terribly tasty. It's not bad (!) and I'll still buy it on occasion, but I'll find myself sometimes not eating the whole amount sent before the next trail town, whereas some other brands (bought randomly in stores along the way) are such that I have to discipline myself to stop eating the stuff.

Their gorp is pretty good, in 4 pound bags as I recall. As with all things you do have to take care to look at expiration date on purchase, and for near-end-of-trip resupply boxes I might vacuum seal some gorp ahead of time too. The biggest issue with their gorp is that on a trip with a number of resupply boxes I can get a bit bored of always the very same type of gorp.

Dried fruit varies, but in general I no longer buy it from Costco, but purchase smaller quantities in a local grocery store. If you do get dried fruit from costco, my suggestion is to avoid the stuff that's a mix of fruit with some nuts and just get fruit. And definitely repackage and vacuum seal; like the gorp, it comes in pretty big bags.

Of course tastes on these things can vary a lot, the above is just my personal biases!
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Brian Lewis
http://postholer.com/brianle