Got any leftover veggies in your root cellar? The kind that are not quite garbage but you're not too excited about eating?
If so... cook them up - separately, or some combo if you think it goes together. No salt or spices. Just veggies and water.
Strain.
Puree.
Line a cookie sheet with foil, spread puree on foil.
Bake at low tempurature, until "dry" but not "hard".
Cool enough to handle.
Cut into whatever size chunks you want (we use "thumb size"... we have dogs that are officially "large" but definitely not the largest)
Cool completely.
Store in freezer.
Our trainer does this, for cheap treats to use when us doggie owners forget to bring ours, or when ours don't work (need a higher-value statement...)
She uses winter squash, beets, carrots, zuchinni, pumpkin, not sure what all else. Doggies particularly like beets (sweet!)