With excellent reputations. Then try using the room safe.  

You could leave them in your vehicle until you are done with your visits.

Limit the number of valuables you bring, stay aware of your surrounding and screen, screen, screen to make sure you are only with reputable guys.

If you don't need it for the appointment, don't bring it with you. Anything that you do need to bring that is of value, keep where you can see. I really can't think of a time that I've needed to bring anything valuable to an outcall, but it's a rule I follow in general.

My belongings stay in my presence at all times. Bathroom run, my purse comes with. It's simple. Unless you guys go in a different room together. Until the person exists the room. Then you run for it!!!!lol jk...not kidding

and some thieves make a habit of targeting provider's guests... sometimes with her cooperation.  Seeing reputable providers/clients in the best way.  
If it's your room, you can hide things, or use the room safe if there is one.  Lot's of places in a normal room...  under or behind furnature, hanging in closet, under the vanity in bathroom, behind drapes...  just remember where you "stashed" them.  
Leaving unnecessary valueables at home is best.

I don't do outcalls.  But for you guys that do outcalls to your homes, good luck.  Just be sure that she is very well-reviewed and above reproach.  Otherwise, you takes your chances......