Kits are great, especially for shorter crops (some of mine are 3-4 days!) But for me, a kit is simply the pictures, any patterned paper I might use, and any embellishments I might consider that are specific enough that I wouldn't take normally. I don't pull cardstock because I like to just take most of mine anyway. I put all of these "kits" in a large ziploc-type bag--I don't use one bag per LO.
Sometimes for shorter crops I will take a specific project to work on because then I can usually take few supplies...in theory!