I decided my little YM186D is too small to mount a toolbox anywhere. And with no ROPS I want both fender handles available and uncluttered, to vault off the tractor if it starts to go over.
So I added saddlebags across the cowl - a multipocket tool scabbard on the left for pruning shears and saw, gloves, and spare 3-point clips, and on the right side
an insulated beer-cooler backback to carry my water jug, tools, and the jacket I shed mid-morning. I also have a small toolbox lashed to the QuickHitch in back. I think bolting on a toolbox back there would be the only place to permanently attach one.
The YM240 is larger and I have two golf bags on it. One on the back of the ROPS for shovels and bow saw. (See my sig photo below). The other carries
chains (for lifting stuff with the loader) and long handle pruners. I first installed this one to make a
scabbard for a cordless reciprocal saw but the saw didn't work well for pruning so that function is superseded by carrying the chainsaw in a bucket lashed to the back side of the front loader bucket, when needed. I also have canvas bags lashed to the ROPS behind my elbows, one for a water jug and the other for gloves and jacket. I hope these suggestions give you some ideas.
As for a drink holder - there must be some way to lash one to the ROPS.