Is there any way to tell what size they are without keeping the packaging they came in? I mean, other than a needle-sizer?
Nope. 
I keep a needle sizer in the case with the needles. I have the needles in the black zipper binder from KP, with the little zipper “envelope” pouches. I labeled the pouches with a stick-on label noting the needle size.
But the needles themselves are not labeled.
I didn’t think so. Thanks! I’m not going blind! Yay!
Nope, they aren’t marked in any way. The sizer is worth the few bucks it costs and it also has features to help you figure your gauge.
I have my needles in the binder but every once in a while i grab the wrong size as I have 2 pairs in each of the little pouches that is divided into 3rds. I’ve got 2 needles sizer/guage rulers. it comes in handy cause I have a supply kit ofr home and one for on the go.
Or, you could purchase a set of CIRCULAR NEEDLE I.D. TAGS , which dangle from the needle cable, or these which snap around the needle cable. That link, by the way, leads to the Knitters Review of them, they can be purchased at most online yarn stores, or at your LYS
The needle gauge is invaluable. Even for needles that are not Options or Harmony’s. I’ve labeled all in the black notebook purchased from Options, one for needles, the other notebook for the cables, but still one can mess up. Go for the gauge.