My understanding is that they won't start to demand glass until you've started to produce glass items (and I've never had demands for any other kind of glass than the standard green one, which is the only one I bother with). Shell demands are rare: I've so far had a total of one, and I managed to meet that one with some emergency fishing (I generally don't fish). You'd have to be extremely lucky to be able to use a snail man shell, as their sentience means they can't be butchered, so the process of killing them would somehow have to remove the shell from them so no butchering would be required (and I don't even know if it's possible to kill something with such a result).
Otherwise, keeping a few of each kind of item 'f'orbidden is a way to ensure you've got a supply, as said by others. I always embark with silk thread, for instance, as it can take some time to get access to that. I did get into a bind when undead were besieging me and I got two moods demanding wood during that year. I was over an aquifer I hadn't yet pierced, so cavern wood was out of the question. I managed to scrounge the material by dismantling a number of workshops (and replace them with ones built from clay).
Moods don't start to happen until your pop reaches 20, which normally means you're mood free until the second spring's immigration deluge, so you should get some time to build up a source material stock.