I am a (male) time traveler who would like to pack a single suitcase with enough outfits to be inconspicuous in as many (past) eras as possible. What should I pack?
Religious clothes. They're traditionally very simple and because they're tied to religious tradition, the styles don't really change much. Wear the clothes of an imam, or a Buddhist monk, or a Catholic priest, or an Orthodox priest… preferably of an archaic style. People in the 21st century would question 17th century formalwear, but probably not the clothes in a style of an ancient monk or priest – they would assume you're very pious and traditional, not a time traveller. As a time traveller, you'll want to pack monk robes – or other religious garments – from whichever cultures you're most likely to visit.
Warning: Be at least a little knowledgeable on whatever religion you're impersonating, otherwise the guise will slip very easily. If you're pretending to be an imam and you drink alcohol, or you're pretending to be a Catholic priest and you start thinking about hooking up with that barmaid... well, the local culture will be very confused. (Well. I hope it would confuse them, and not make them avert their eyes. I guess it depends on how much the people trust the clergy/religious leaders in the area.)
But the benefits here outweigh the costs of a little learning. While you'll want to take the religious clothes of numerous regions and cultures, which may be rather tight, you'll be able to wear them across a wide range of time periods. You'll also be able to fade into the background. Except when people start coming to you asking for personal advice, which may ruin the timelines, so be careful.
How big is that suitcase? And do you have to cope with different climates and regions?
- A leather jacket. Something like that has been along for a long time. No zippers ...
- A collarless shirt.
- Plain leather shoes, plus leather sandals.
- A pair of blue jeans, can be worn after 1880 or so, and/or white/bleached cotton dungarees.
- Leather trousers, for the time before jeans.
- A tunic and trousers.
- A cape or cloak, if there is still room in the suitcase.
That should be a start in moderately European regions.
You could theoretically get away with a bathrobe. Bathrobe-style clothes/bathrobes have been around forever, so you could just wear that. But on a serious note, I would pack the following:
1 black Tshirt
1 pair of jeans
1 pair of sandals
1 pair of burlap pants
10 pounds of bacon jerky (HEY, you can't live without bacon...)