Just found this thread. Pretty spiffy tractor!
My first thought was hand tools, too. I guess my most useful and therefore favourite(?) garden tool would be my DeWit five tine claw/cultivator. It has served me very well since I started gardening, and I would buy it all over again in a heartbeat. However, it soon many have some competition for the top spot on my favourites list.
I just ordered the Root Slayer trenching shovel. After digging out some Saw Greenbriar Vine recently, and knowing that it may come back, not to mention the fact that I have an entire bed I would like to get started either this Autumn or next Spring, I thought the Root Slayer would be an excellent investment, and it is on for $20 off at the moment. I cannot wait to try it! I have some areas right now where I can use it right away, e.g. a trash tree that was cut down a few months ago but insists on coming back again, and again, and again. I hope the Root Slayer will at least let me slice through some of those roots and slow it down if nothing else.
https://www.amazon.com/dp/B01M1CCIWH/