I went through the same experience when I was doing my startup. The biggest problem I found was going to the washroom. I was always afraid someone would highjack my stuff so every time I went to the washroom, I had to pack everything up and bring it with me. This was pretty annoying. Also, if the coffeeshop is busy, good luck finding a clean toilet to sit on.
Maybe I'm overly trusting, but I just ask someone who has line-of-sight, "excuse me, would you mind watching my stuff for a minute?". I figure that the odds of picking the one person who would steal things is very low, and people see it as a gesture of trust. It's sometimes an opening for a conversation when you return, or at least for returning the favour.
"I was always afraid someone would highjack my stuff so every time I went to the washroom, I had to pack everything up and bring it with me."
If you feel like being social, this is a good excuse for striking up a conversation with someone nearby who seems interesting. Ask if the person can keep an eye on your stuff for a few minutes. Assuming he/she is friendly, after you get back and say thanks the ice will be broken and you can chat if you want to. I suppose it's still a bit riskier than taking your stuff with you, but seems minimal.
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.
I use a hybrid version of the technique recommended by the other responders to your comment: Take the big hardware with me, and ask my neighbor to watch the remainder of my stuff (usually my bag, power adapter, and a couple of sketchbooks). It's just imprudent to leave two grand sitting out on a table, IMO.
As for restroom cleanliness, worrying less about that is one of the many benefits of eliminating caffeine from my diet ;)
