Neither had I until recently.
Since I bought the van last year and got it on the road this summer, its had a plastic "get you home" style fuel cap on it. You know, the ones that you can't lock or leave your keys in to remember you've left it on the pump!

Well having had a bad day at work, I popped by the petrol station to get £20 of diesel, ripped the badly fitting cap out and threw it in anger on top of the fuel pump. Having juiced up and paid off I went.
So off I go, round a roundabout and do a 270 degree spin on my own diesel slick, taking out a small sign in the process!

Came to a stop, facing the outside of the roundabout, took a look at the now crippled sign on the roundabout, not hanging about longer than I had to steered hard right and off I go. Woooops!!! Probably lost about £5 of fuel and felt rather guilty about leaving a slick on every right hand corner on the way home. I only realised i'd forgotten the filler cap when I got home, wondered how I managed to spin a transit on a hot sunny day!
And the ironic thing? I've been driving round for about a month or so with a Capri locking fuel cap which i've now found out just happens to fit!
Moral of that story??? Being a cheap b*stard and not forking out for a proper fuel cap costs fuel..................and sign posts!!!
Guy