I don't think there is a particular trick to fix that, here's what I do - if the place is in a decent neighborhood and there are other people on laptops around, I'll ask someone to watch my things.

The trick I use is to pick someone that has line of site on my things, so they pay attention even if they don't mean to. And ideally to pick someone with a laptop, and preferably a better laptop than yours, that makes them a tad more trustworthy, because at least they probably won't take off with yours.

If the neighborhood is sketchy or there is no one around, I take it with me.