Some pieces of gear you never regret buying, a great pair of trainers, a comfy pair of socks, my wind briefs.   I bought the Brooks LSD jacket on sale for something like $20.  It stuffs into its own pocket, it is windproof (wore out in the North Hills today and when layered it works like a charm), will fit in any bag, and is now a part of my kit whenever I go for a run.  Just in case.  Breathablity of the jacket blows, but for the price and functionality it is a hard one to beat.

Bonus favorite thing.  Training partners. They get up early.  They run in some of the worst conditions imaginable.  They keep you motivated.  Never underestimate the power of a solid crew.