Goats rotated in after cattle seems to work pretty well, since the goats readily eat (and prefer) a lot of the stuff the cows have no interest in. One of the formerly active posters here (Alejandro delaGarza) ran them together down in Mexico with good financial success. Were it not for fencing issues, coyotes and being an absentee owner I sure would have given goats a try these last few years. Sure could have cut down on my Remedy and diesel bill!
As to other enterprises, I know a couple of guys that do as Texan mentioned, but these are not the hobby boys that Caustic referred to. They're essentially pretty much full time into agriculture and they do some custom hay work after their own haying needs are taken care of. In addition, they will do custom hauling of cattle and hay, one of them does a little order buying and also a fair amount of shredding & dozer work, one does a good bit of contract fence building, etc. They pretty much will do custom work for all the weekenders, small timers or old timers that can't do it anymore --- but only as their schedule permits after taking care of their own needs. These guys love the ranching and related agribusiness lifestyle, and they've already got a lot of equipment anyway so these are logical pursuits to bring in some extra cash.
Of course in much of Texas the primary extra enterprise is leasing the land for deer, dove, quail and waterfowl hunting. I think folks in many other states would be astounded to know how much $$$ many Texas ranchers get for those hunting rights.