This girl was on the back of her boyfriend's bike when they went down. No gear. Helmet only.
" I noticed that my knees were uncovered when the little pieces of what I thought were gravel scraped against my skin, only to find out later that they were my actual kneecaps grinding against the pavement below them."
One more thing to think about: when I was in my rider training course they told us what kind of equipment your passenger should ride. It should be the same, or better than what the driver has.
If you have a leather jacket and your passenger doesn't, give it to them. Same with leather gloves. Boots and pants won't fit, but I know I would ride a lot more cautiously if I was only wearing a t-shirt.