Maggot,

Even the plastic bag or plastic wrap around the fishing worm is not going to prevent the plasticizers from moving into other plastic items it is touching. Phthalate esters are used in plastics to control the softness. These are not part of the plastic structure, but more like dissolved in the plastic base, so they tend to evaporate or move around. This is why plastic gets brittle with age....the plasticizer has migrated out. Wrapping the worm in foil would be better, but even this will not prevent the plasticizer from evaporating and potentially changing other plastic items in the kit. Like Max said worms have loads of this chemical....excluding them from the kit would be my recommendation. I recommend adding wet, dry, streamer or nymph pattern flies.

BTW phthalate esters plasticizers are detectable in just about every sample of water, soil etc found on earth now.