Nah, if the temps are in that range and it's going to rain, I'm just not going out. Somehow, rain in 30-40F weather is worse than biking while it's snowing. I would much rather bike through a 2-4 inch snowstorm than through 35F with rain.

To answer OP's question, my light jacket fits nicely in my center jersey pocket with my mini-pump & multi-tool; the trick is to roll the jacket up and tuck about 2/3 of the rolled jacket into the pocket. If you try to cram the entire jacket into the jersey pocket, that's when it can get uncomfortable. Left jersey pocket is for snacks and keys. Right pocket is for ID, phone and extra snacks if needed. Spare tubes, tire levers, and CO2 gimmicks are in the saddle bag. I like the Arundel saddle bags because they attach securely, hold everything I need them to, and look nice.