Any of the "deer plot" or "hunter's plot" mixes are great for overseeding your grassy areas. The stuff is meant to grow FAST and is super palatable to deer, and so rabbits. Most of the mixes contain quick growing annuals, and some perennials. Most also are usable as winter cover (putting nitrogen back into the ground).
I've used a local deer plot and another for turkeys for a few years now. good stuff. The one I use also has turnips and field peas in the mix. All you really need to do is rake into the ground enough so you have a bit of a "furrow" for the seed to fall into (if you're doing a small area). Larger areas, just broadcast it (throw it out with your hand) and then water the area.
when "over seeding" you don't need to go with the "XXnumber of pounds per acre) number. What you're trying to do is give the grasses some extra STUFF. (although it's easier to get it growing if you have a freshly tilled area without grass competing for the clover, etc.)
It does keep for a year or two if you keep it dry. OR you can keep extra and sprout it in the winter months. clover and alfalfa sprouts is a good thing. or just plant a few containers on the porch for winter harvest.
