I use a layer of paper towels with a layer of rubberized shelf liner over the top of that for the first several days, and usually a clean soft towel at one end under the lamp where they all sleep. I change it all daily, or twice daily if I have a big batch of keets (I usually get 10-12 rolls at the dollar store, cut it to fit my brooders and will wash it after it's soiled and use it again and again thru the hatching season). Just using old towels (with no loose strings) works great too, and it's always cheap and easily to get a good supply of them from thrift stores. Some just use paper towels that have good texture to them so they keets have good traction. I have done this too, but prefer bedding with better footing so nobody slips and injures their legs or tendons. Splayed leg and slipped tendons is painful tot he keets and time consuming to correct... so I try to avoid dealing with injuries at all from the get-go. Keets poop a lot starting by the 2nd day and can get a build of of poop on their feet that needs to be soak/washed off with warm water if you don't change out the bedding often enough.
After 3-4 days of using the shelf liner and towel (and I see that they are all eating and drinking well) I switch to using coarse straw or grass hay (I make sure to use hay that has no seed in it). It helps to refill the keet's feeder a little before you change out the bedding to straw or hay, that way they all chow down and will have full crops and are less likely to try eating the straw or grass. Occasionally I do have to pick up a keet and pull a piece of straw or hay out of it's mouth tho... they get all excited about the new bedding and run around with a piece of it like it's a prize worm they don't want to share with the others, and try to eat it down before anyone can take it away. Usually they tucker themselves out after a couple hour or so of running around excited, and it's not a problem after that... and as long as I use their same feeder they remember THAT'S where the food is and they leave the straw and hay alone.Plus after several hours of running around they have all the bedding trampled down smooth and it's less enticing to them.
Hope that helps.