Go to the baking supplies at your local grocery store/supermarket. There will be boxes of unflavored gelatin mix.
I used small "party ice" trays to make my cubes. I used dried bloodworms, ground smelt, and crushed algae wafers & shrimp pellets. I mix the ingredients with gelatin and a bit of water, then freeze. Bugger fish will swallow them whole, but smaller fish will peck the hell outta them.