Sometimes when I buy (cheap) gummy candy, it's a little too hard to enjoy. Is there a way to soften them? Preferably something that lasts, as opposed to perhaps heating them and eating them while they're warm.
Gummy candy is essentially just water, sugar, gelatin, and a few other additives like food colouring.
Gelatin's gel strength1 is partially dependent on its concentration. The more concentrated, the harder it gets. Gummy candies left sitting around will lose water due to evaporation, which makes the gelatin more concentrated and thus harder, and if you watch carefully you'll notice that the moisture loss also makes the gummies shrink.
To soften them, you need to rehydrate them. Toss them in a bowl of hot or warm water (don't use cold water - gelatin is only soluble in warmer water) until they reach the desired consistency - usually around 20 minutes or so. The longer you leave them in the water, the more water they'll absorb, the more they'll grow and the softer they'll get.