In my experience, one can never have too many ratchet straps of different sizes: they are good for tying down aircraft, strapping down cargo, hanging a hammock, pitching a big tent, improvise all kinds of slings, you name it. Just got my fix at Action: 25 mm wide, 250 kg max load for €3, 38 mm wide, 1000 kg max load for €6 and 50 mm wide, 2000 kg max load for €11. Decent quality, EN 12195-2 conformant.
One of my favourite knots:
