All my tractors have their "oem toolbox" which is generally smaller than I'd like. Those boxes get the small stuff. Linch pins, a roll of baling wire, a roll of electrcial tape, a couple screwdrivers, channellocks, a cresent wrench, a pair of fence pliers, needle nosed vice grips, hitch pins, a few odd bolts/nuts/washers, a couple shop towels, and the obligatory hammer.
One of the things that John Deere offered over the years that I've come to ADORE is the toolboxes that were first offered on the 30 series tractors in 1973. It's about 8" X 9" X 18", with a lift out tray, and a VERY secure mount that allows the box to be removed with the pull of a small pin. I've adapted the mount so that they'll bolt on to every tractor I own, then each tractor has it's own "permanent" mount installed. . I keep one box filled with baler items, one with planter parts, another with sickle bar stuff, one with fence building junk, ect..... Altogether, I've got 7 of these "use specific" boxes ready to slap on the tractor of the day and head to the field. The right tools go with the right implement that way. No need to carry everything or search from tool box to toolbox to find what I need. Nothing like being able to fix things in the field and NOT have to drive back to the house every time something goes wrong. I even keep old copies of manuals in a few tool kits. (i.e. baler) I've even got one box stuffed with "chainsaw stuff" for wood cutting season.