From my vantage point, farmers are a lot more concientious about cleaning up equipment before storing it for the winter than they used to be. I used to see combines parked in machine sheds that looked like they had loose straw stacked on their rear decks, and planters that had a couple bags of seed still in the seed hoppers. Today most machines in machine sheds have been blown off, washed up and lubed prior to storage.
But there are some areas that often get overlooked. On combines, rock traps are easily overlooked, as are sumps at the bottom of vertical unloading augers, clean grain elevators and tailings elevators. Since all those areas are "low points," any water from washing the machine, or any rain that fell on the machine during harvest, accumulates in those areas. If they aren't cleaned out, by next summer each area will be packed with a lovely mass of rotting grain, resting against the bearings and shafts at the bottom of those augers an elevators.
Planters have sat in the shed for several months by now, but if there's any seed left in hoppers or bins, it's an inviting target for mice and rats. When living was easy last summer, the varmints may have ignored that treated seed, but this winter when food is harder to come by, they'll be glad to set up housekeeping inside seed tubes or planter frame tubes. If they get bored, they're plenty of wiring harnesses routed through those areas that they can gnaw on for entertainment.
Sprayers don't have much attraction for varmints, and by nature don't acquire much crop debris, but the very chemicals they deliver can harm them during storage. It's a no-brainer to drain the spray system AND flush it with RV antifreeze. Sprayer manufacturers say that it's best to flush with antifreeze because merely draining risks "missing" low points in valves or controls that will then freeze and damage the component. In most cases, manufacturers also prefer to have spray pumps and valves stored "wet"--as in, with liquid in them--to keep seals from drying out.
Tractors benefit from a good cleaning before storage, and any self-propelled machine benefits from some sort of plan to keep batteries charged. Whenever a battery's internal voltage falls below 12.6 volts it's possible for sulfation to begin. The best way to keep batteries at optimum charge is to hook them up to small, computerized "float chargers" or "battery maintainers" that constantly monitor batteries and keep them properly charged. These little gizmos aren't extremely pricey--from $15 to $50, depending on the size of the battery to be maintained, but when you compare the one-time price of a maintainer that will last many years to the $200 price of a large battery that was allowed to discharge and fail...
Don't forget to prep your summer toys for winter storage. Motorcycle batteries, motorcycle cooling systems, boat starting batteries, boat trolling motor batteries, boat bilge pumps, boat live well pumps--they all benefit from a little preventive maintenance.