Ever tried keeping insects you find in the garden, or any small animals in general? I've always had an interest in natural history ever since I was very young. Identifying the species is the most fun for me, you need to know the diet and habitat of what you've found to correctly provide for it. Just go out and scoop up whatever looks cool, preferably an active hunter, wolf spiders are a particular favourite of mine due to their hunting behaviour (they don't just sit in webs). All you need is a plastic container. I've kept all kinds of species of spiders, worms, beetles, fish and ants. It is surprisingly relaxing observing what you have caught.