Everything is a potential clay tool. Before i throw anything away i look at it and say will this make a good impression in clay? A trip to the dollar store, hardware store, kitchen gadget store and of course the thrift store can net you a bevy of new tools.
A tool story: i teach handbuilding to adults. I had a student wanted to make faux driftwood from clay. I told her i had the perfect tool to make bark and headed out the classroom door. She thought i was headed to my truck to get a tool but instead i came back in with mulch chunks from the plant bed outside the classroom. They made the perfect bark texture and the perfect broken wood texture, the best tool for making faux driftwood you could find.
Now the most unconventional tool...i'm stumped...i don't know what a conventional tool is. I use a lot of random objects...pen caps, toy car tires, a tangle of jute, the bracelets i'm wearing, screws, springs, twine wrapped dowels, shells, pasta, ferns, strings of beads, keys, rope... hold it i know....my most unconventional....gutter guard...its a diamond patterned wire mesh that comes in small rolls to lay on top of your gutters to keep leaves out...makes great scale patterns when making fish or a background lattice pattern when using a floral theme.