Fluval bug bites are my weapon of choice on the dry food side. They do a few different varieties, but for smaller fish the smaller tropical granules are good:
Fluval Bug Bites Tropical Granule Fish Food 45g
Amazon product ASIN B07194GD1F
They do tend to sink quite quickly though, so I’ve recently been trying the colour enhancing flake variety. Crushed between the fingers and sprinkled on the surface, it’s perfect for small surface feeders like chilli’s as it stays there for some time giving them time to pick at it. They really seem to like it.
Fluval Bug Bites Color Enhancing Flakes 45g
Amazon product ASIN B0874XYL3K
For live foods it’s hard to go wrong with a grindal worm culture, which you can source on eBay or from a member on here. I’d offer you some of mine, but I’ve just split my culture to share with another member. You can also hatch live brine shrimp which the fish go mad for also.
Live foods from water butts during the summer work well too if you have one, or set up a plastic container with some dried oak leaves in the bottom in the spring if not. I did that this year (as I don’t have a water butt), set up a 70 litre storage box in the garden and seeded it with some hatched Moina, and it was really successful and productive.
I don’t use frozen food, I always find they’re too big for my fish, so someone else will need to help you there with some suggestions.
The snails can likely exist on whatever is in the tank, though if you end up with a large population of them, you can supplement with cucumber slices and Hikari algae wafers.