Even at flexible workplaces, it's hard to find a place to nap unless there is a free room/couch somewhere. I tried taking a nap on a bench at Yerba Buena Gardens once but was kicked off the bench by the Park Guardians. :(

When I can't fit in a nap, a brisk walk gives me a good energy boost or even switching to standing at my desk... in fact, I'm about to switch to standing now. Have you tried that?