Don't know how many minnows you have but seems like if you change the water completely everyday that should be ok. Otherwise you will need a filter.
keep the water aerated, keep water clean, feed the little critters to keep them fat and sassy, and keep the tank clean. Most of all keep the water coolwith plenty of oxygen.
Keep the minnow tank water cool and let it warm to the lake water temp as you travel to the lake. Cooler water slows the minnow metabolism so bodily functions slow down.
good luck on keeping them, I do real well with a ten gallon bucket a cheap aquarium aerater and a fillter that I found will faten on the side of the bucket. I can't keep them in hot weather very well ( no cheap way to cool the water) but I well from fall to spring here in NC.