Disclaimer: This project veers a bit into old-lady-who-saves-margarine-tubs territory. There, you've been warned.
I needed a watering can, but couldn't bring myself to spend money on one. I couldn't wrap my head around the thought of buying a plastic container when we recycle so many plastic containers.
I took a small laundry detergent bottle and rinsed it out well. This detergent is biodegradable, so any trace amounts left in the bottle shouldn't hurt the plants.
Then I drilled three small holes in the cap and a larger hole in the bottle itself above the handle for air. The whole thing took like 90 seconds!
Quick, easy, functional, re-used and best of all free!