I think that walking on the blanket is rude, I'd be tempted to just ask please not to!
As for sucking fingers with dogs etc, well DS I found sucking my dog's tail yesterday, (doh) and eating my uggs. (ugh!!!!!!! gross!)

I do think a little bit of germs are good, but in moderation, and something that I know is kept relatively clean - a cafe is a bit too much, don't know enough of who was at that table before, or even if it was clean!