I travel light these days, multitool, the usual flat stuff etc. I've never needed any chain links nor the chain tool so I even leave that off.

Some things that I don't carry, but sometimes feel like I should: lighter, Mylar space blanket, flashlight, wipes, spokes, chain oil. Reading glasses. De-icer would have been smart a few times last winter. First aid that I could have used a couple of times: bandages, Tylenol, sling, gown (what they charge for that stuff in ER would make it worth it)