I keep a number of small tanks, but my utility tanks and buckets really help me balance my hobby. These three 3.5 tanks are always cycled, and can host plants or fish:
One is a previous organic soil Betta tank. The next is just mulm, filter, and light. The third adds plants and wood.
This bucket setup includes an off-gas bucket, a plant/wood staging bucket, a last-chance bucket, and with a fine sponge pump, a garden bucket. The tiny pail is for my cat.