You need to learn what works best for you. Some people run in shorts and no shirt in the 20s. At that same temp others are bundling up. If you have been running long enough you should have a feel now for what is optimal for you. One option is to layer and toss stuff.
I do like the guide of "if you are not feeling cold at the start you likely are not going to run a good time". I have gone to the start line in a large garbage bag (usually when raining) so I can toss it aside. I have gone to the start line wearing an old sweatshirt (I even bought one for $5 at Salvation Army just to toss it---no way I am tossing a sweatshirt I actually like).
I have worn cheap cotton gardening gloves in races as well. I think I got a pair for $2 so if I toss them no big loss. If it is dry out, they work fine for me. (And pay homage to Bill Rodgers at the same time.) Hats or head bands too.