When that kind of thing (never the whole bunch of stuff under the carriage, but a few items) has happened to me I just go back. I don't want the store "ripping me off", so it's only fair that I don't do that to them. Once, a couple of years ago, I did discover a small, $1, notebook that had fallen through the baby seat. That time I couldn't be bothered going back. I told myself they've kept enough of my stuff that didn't get into a bag, and I couldn't be bothered going back to get it either - so I figured, "why be a fanatic about a dollar item?" (and didn't bother).