Do not feed them if you're going to go again soon. 1st most people over feed and wasted food creates ammonia which kills. 2nd, fed fish poop which also fouls water. They can go a week w/o food easy, a lot longer in winter. If you're not going again soon, dump them on bank, salt if you're inclined. Search but basically, you layer in salt - too much bother in my book.
Crappie and bass minnows -Once it's warm, it's tuff. Focus on reasonably coolest spot avail. Prior to the end of May, keep in a cheap styrofoam minnow bucket. Bigger round ones not the little square jobs. Tired of styrofoam ones cracking, leaking, etc and don't want to shell out for a pricey Frabill - Nest it in a 5 gal bucket, preferably white so it absorbs less heat. If transporting in a truck bed, you need a chunk of wood, rock, or ice/snowballs in winter so top doesn't blow off. Check and remove dead at least 1/day. Do about 50% water change periodically. EDIT: Yellowish or smelly water means it needs changed. Local City water is fine if you let it sit 24 hours in open bucket. Assuming this is in a garage, do water changes in morning so water in make-up water bucket is cool. Huge bonus points for an aerator pumping cool air but don't let it beat minnows. It doesn't need to be on bottom of bucket.
Now, a key thing is taking care of your minnows while fishing. Keep them cool (Styrofoam and change water as it warms or good old bucket in lake/stream water). If you beat them up catching one to bait hook, you will have more mortality later. Dead minnows foul water (ammonia) and it's all over. So, bit of a bother, but if you plan to keep leftovers, scoop out 1/2 dozen at a time and keep in a separate bucket to fish with.
If you're a crappie fisherperson. Buy less minnows, get a pack of waxworms and a few 1/32 oz white marabou feather jigs and a few 1/32 oz grub bodies of your choice. If you're catching enough to run out of minnows, they will hit a jig/waxworm. If your bobber fishing, twitch and pause. If your vertical, vibrate. Now, if the crappie or gills are not jumping on the jig, try using two hooked through the head/collar. Double waxworm on ice jig is best thing ever ice fishing gills too. Waxworms don't take up much space in top of refridge door.
Chubs, sucker minnows, big common shiners and gills need a decent size cooler and aerator.
Good old metal bucket with holes in it submerged in a cold creek beats everything. Hide it. If the water is dirty in the local river and you're coming back before the next rain, submerge it with a big flat rock on top in an out of the way place. We used to store crayfish that way too. Shaded water feature pool in yard with circulation is a winner too.
Recap - cool, prevent and reduce ammonia through water changes, removing dead, and to a point aeration. Don't beat them up. Doesn't matter how you accomplish it. Generally, if you have left over minnows, it is necessary to go fishing again very soon so they don't die and go to waste. Your obligated to not waste resources. Keeping them more than a few days is generally not worth the bother after early May. By all means try, this is how we learn. One thing you will eventually learn - stuff gets stinky fast in warm weather if you don't check frequently enough to remove dead

Regards