as a modder myself, i feel like we could use more tags for creatures and entities, as well as some for plants. Along with these I'll give examples.
Creatures
PARASITES_RAW: When a piece of meat from a creature with this tag (large freshwater fish, most land animals) is eaten, theres a chance that a fish can contract parasites. Perhaps these parasites can be their own creatures, whom give syndromes when consumed using a complicated extra set of tags.
PARASITES_HAIR: this creatures hair or fur can attract parasites like lice, fleas, and ticks.
VERMIN_PARASITE (with variants for meat, hair, and more): this vermin latches onto creatures often in general, but occasionally specific, often sucking their blood, and lives off them for most or all of their life.
NEEDS_BALANCED_DIET: A tag for humanoids only, NEEDS_BALANCED_DIET is a tag that makes it so by default, creatures no longer get a negative thought from eating the same gruel and drinking the same booze every day. Instead, a creature without the tag functions like one now, minus those unhappy thoughts, while one with this tag can not only get unhappy thoughts, but minor negative effects (or even major), if they dont eat a varied enough diet. Personally I'd make a balanced diet depend on the later-mentioned FLAVOR tag.
Entities
PRECURSOR: An entity with the tag "PRECURSOR" creates sites rapidly in the first days of history gen (Or even before history, but that weould be complicated), then immediately dies off either at the end of year 1, or preferably, in the complicated solution, before history even starts
Plants
PARASITES: Similar to the meat parasites thing, some real world plants tend to have parasites when raw. Why don't i just use syndromes? Because I'm pretty sure syndromes would apply when cooked too.
DESCRIPTION: Honestly its wasted potential that plants dont have descriptions, and they could really use them.
Materials (as in the ones that plants, creatures, and more use)
FLAVOR: Requires the template to be edible by default. The FLAVOR tag lets you determine what a food tastes like. Some dwarves prefer certain flavors and combinations, and a mix of flavors in a dwarf's life will allow them protection from blandness induced negative thoughts, while also giving them positive thoughts.
Feel free to add on to this with your own tokens.