Well, you could remove an friend's appendix with a pocket knife, sharpened spoon, and vice grips after knocking them with a bottle of whiskey...in the mouth and on the head, and then sew them up with sewing thread, but there's nothing quite like having the right tools for the job, and if you do collect or buy and sell instruments with any frequency, then the tools will pay for themselves sooner than later. I've seen all sorts of suggestions like using welding torch tip cleaners as nut files, etc., etc., but you get better results faster with the right tools. To do most basic nut and fret work on ukes shouldn't cost more than about $100.00 for good tools from StewMac, and they'll last for tens of years.