I completely understand your frustration, I have a son with ARFID and 100% understand the need for brand specific things. I often bring boxes of pop tarts, nutrigrain bars, fruit cups, in very specific brands and flavours. Lots of people just don’t have the knowledge about different eating disorders. I don’t think you will have a problem at all, as long as they’re in sealed , unopened containers. I would just pack them and carry them on and if anyone gives you a hard time, tell them about the eating disorder.