Someone mentioned this, I'll mention it again. Tools, for me that was mostly sockets and ratcheting wrenches (two), because none of my tools, not even my biggest adjustable wrench, could fit some of the larger bolts on the tractor and/or attachments.
I bought a set with paired shallow/deep sockets (was reasonably priced set from Home Depot), because sometimes you'll want the same size socket on both sides of a nut/bolt situation (which means you need two wrenches, I had a spare from somebody's grandfather, don't waste nuthin!). Not sure about your brand of tractor, but with Kubotas it's also important to have both SAE and metric, because the tractor stuff tends to be metric (made overseas), and the attachment stuff tends to be SAE (made in the states). It sucks to be missing the size you need when you need it. Sure, I have a bunch of sizes I don't need, but the set price was so good, compared to buying single sockets, that it was not extravagant.
The only other thing I'm betting nobody mentioned was ... an air blower, like a leaf blower. Because if you're out in the field cutting weeds in the fall that dried pollen (e.g. golden rod) will jam your air filter and coolant fins mercilessly, and you absolutely cannot touch those fins or you'll bend them, air blower is the way to go.
