Late to this but yes, ditto everyone who's recommended merino. Stays un-gross so much longer than cotton or synthetic (I've not been impressed with most of the anti-microbial treatments for synthetic sports gear). For outdoor travel, I take merino tees, undies, bralettes, and socks. I only do synthetic for pants/shorts. Then I add a puffy, fleece, or wool sweater for insulation, depending on circumstances, and a Goretex shell.
For plain old city travel, I have no qualms about re-wearing tees once or twice, regardless of fabrication. I don't sweat much unless it's super humid or I'm really exerting myself.
And how fun to have an unplanned YLF meetup at REI!!