Like cone wrenches, there are some inexpensive and affordable bike tools for which there is no substitute or makeshift tool that won't drive you daffy.

For bikes with threaded bottom brackets (most older bikes and some contemporary models), a good forged lock ring spanner with properly squared business ends to avoid slipping. The Holy Grail is the Hozan Rock Ring, cycling's finest example of Japangrish manufacturing. When my LBS offered to sell me one of theirs I pounced and happily paid the $20. But the later, unfortunately spelling-corrected Hozan Lock Ring wrenches, are just as good. You just won't giggle internally like a first grader while using it. Not that I still do that. Okay, I'm doing it now just thinking about it.

For freewheels -- still surprisingly common even on some newer bikes -- at least two sockets for the most common versions: one for Shimano and a few others (splined, a better design); one for Suntour four-prong, the most common later Suntour freewheels. Eventually you might need the older Suntour two-prong socket. None of 'em cost much and, like skinny cone wrenches, there are no substitutes or makeshift tools.