Plant tool you cant live without?
The only tool I use currently is a pair of 12 inch stainless steel tweezers, it took me a while to figure out how to use them well but now I wouldn't plant a plant with out them!
Stainless steel scissors are nice, but the pair I bought a few years back dulled really quickly so I get my scissors from the dollar store and toss them out when they rust or become dull.
A water changer is a really good thing to save up for, as well as a pump. Currently I have my RO/DI system set up in the spare bathroom in the tub, it saves me a lot of time because I can drain my tank with the water changer and then just pump water into the tank. There no more lifting buckets of water or any of that nonsense.