I too have had pilot biscuits AKA hardtack in MRE's (solo, things apparently haven't changed much since the 60s) They are terrible. Original hardtack was designed to be soaked in grog (rum cut 50/50 w/water) to soften it up so keep that in mind while ingesting them. I'd suggest soft taco shells or pita bread. Keep in an air tight container and you should be good for 15 days, just make sure its the last item you buy and make sure it has an expiration date close to your 15th day (or beyond, I dont really know how far out they put expiration dates on bread).

Another thought is bringing bisquik type baking flour to make breadish food for pb&j....not sure what the weight to produced product is on that, but it might be worth looking into