The vast majority of food items at the kiosks will be considered snacks under the DP. No alcohol/wine/beer will be eligible as a snack credit.
Once F&W begins, most bloggers will be out in the first few days taking video/pics of the new kiosks and the menus. Keep your eyes open for eg the DIS Team's coverage. This will make it easy to know which specific snacks you want to target.
Kiosk snacks have the same purple snack square that you see on all WDW menus.
Any snack item over $6 is a decent use of your snack credit. Any snack item over $8 is a great use of that credit.
In addition to using my snack credits, I buy a F&W wristlet gift card and load it with eg. $40. When I find snack items under $5, but still want to sample, I use the gift card to purchase instead of burning a snack credit. This also gives me a mini budget so I don't go crazy with cash at the kiosks.
Another tip is, if possible, schedule another Epcot F&W day toward the end of your vacation. If you have a large number of snack credits to use up, you will at least get one last kick at the can to spend them at the kiosks before you leave.
You can buy the wristlet gift cards at the Festival Center, usually at the 2 Bridge Kiosks and also (where I get mine) in the Festival Shop on the lagoon side in World Showcase between Mexico and Canada. A pet peeve of mine is that WDW does a poor job telling guests where they can buy the cards and even that the cards are available.
