I'm not close to passable yet, so I have no choice in the matter unless I go out in "man drag" (not fun). When I am more passable, I want to engage in activism, but I have no desire to announce to every stranger all the time either. For me, the decision to disclose trans status would depend on how relevant it would be to whatever I was engaged in. freinds and romantic partners, yes. The pride parade yes. Sticking up for another person being mistreated yes.
the grocery store buying hummus and pita, no, unless there is a good reason. I think for me, I want to look passable, so I can feel right when I look in the mirror and hear myself talk, but would be fine with being seen with poorly passing trans-women. I don't mind the trans label, for me, it reflects that I had a different set of life experiences than most cis-females and a radically different emotional/mental life than cis-males have ever had.