aerator ?

walmart is your friend.

The portable ones are nice for the car or camping trips.  If you are keeping them in the garage, you'll probably want to get a plug in model with a long stone.  I kept shiners in a "beer keg" tub (I think 20 gallon) for about few weeks, using an areator and filter from an old aqurium.  Chubs might need a bit more though?  Make sure you put a screen on top too.  They will try to jump out.  The more water you have, the better chance of you keeping them alive for long.

Wal-Mart now has "Hush Bubbles" bubblers for around $15. Do yourself a favor and buy this pump. It is the quietest running pump I have found. The cheaper ones will drive you nuts listening to it run. 

I know one thing we stumbled onto that has helped us keep our bait alive longer is to use a big old cooler as our 'bait well' at home. Water temp seems to remain much more stable and definitely cooler during warm weather. We use a plug in aerator and change out about 1/2 of the water each day depending on how many fish we have in it(we see a lot more 'die off' if we crowd the bait at all). We have also used a pump system with an aerator 'bar' that sprays multiple jets against the cooler wall to provide the bubbles/air for when we have lot of larger baits in the cooler. When we are ready to make a trip out we put fresh water in our minnow bucket and let it set so the temps aren't too different (to prevent shocking them too much) and then use a battery bubbler from WalMart. We have had pretty good luck with everything from minnows to chubs and blue gills with this set up but we don't normally keep bait for longer than two weeks at any given time. I think if you are keeping baits longer you may need a filter system and that's out of my range of experience.

Definitely need to change water as well as aerate! Fish poop & pee which affects water quality and if you feed them the food ferments. As mentioned coolers work well for longevity, along with oxygen and clean water!