I've made many fires with magnifying glasses and with fresnel lenses (super easy to slip into your wallet). Also, with reading glasses (or any glasses made for farsightedness) and the lens from the big end of my spyglass. (Lenses almost feel like cheating to me, because that's so easy.)
You can also use really clear ice, water in plastic bags, and water bottles full of water-- anything which will focus the sun. I've never done those-- never tried except for the plastic water bottles (and it didn't work for me).
If you could find a chunk of broken glass that would focus the sun, it would work. I'm guessing that might be hard to find.
I have an antique glass paperweight that I may just have to try. Thanks for giving me the idea!