"In Renaissance Turkey, many crossroads saw vendors selling "fragrant bites of hot meat", including chicken and lamb that had been spit roasted." (Mary Snodgrass (2004-09-27). Encyclopedia of Kitchen History.)

Here is a link to cooks who published cookbooks, some of which are late medieval, others renaissance: http://www.oldcook.com/en/medieval-discovering_cooks You might be able to find translations for some of them.

In Tuscany, there is this street food that supposedly has been around for ages. It's called Lampredotto and is basically fried cow stomach with herbs served in bread. According to the wikipedia link above it's been around at least since the 15th century.