Veggies are a good calcium source. Zucchini is great as well. I just nuke it until they sink. More nutrients are kept in. I've seen a lot of people stick a fork into the veggie and drop it in the tank raw..easy to remove that way.
My snails don't touch any veggies.. :S
Lots of calcium is important for thick shell growth. I use tums..just drop it in and they both are all over those. I've found the generic brands don't dissolve quickly so your water doesn't cloud up.
You can use cuttlebone as well. I just got some but haven't tried it yet. Apparently if you boil it, or soak it, it will sink.
They are messy creatures...I use a turkey baster to suck up the poop in between water change days. They tend to poop where they eat. If you put your food/tums in the same spot everytime, their mess is pretty easy to clean up.
Enjoy your snail!! I think they are super cute. :)