Last week I tried this frozen treat idea with my 4 and they loved it.
Tools: Ziploc Bag. Water. Goodies.
(For medium to large dogs) Take a ziplock bag, toss in a few goodies such as 2 baby carrots, small pieces of some pupperoni, a couple table spoons of wet dog food, a few kibbles of dry dog food or other treats that they like. (Just a dab will do ya) Then add in some water. You can also add a little bit of Tang or Crystal Light sometimes. To keep variety some days fill it with a lot of water (make a big block) some days just add a cup or two. When you fill 1/2 a bag or less you can place it different ways in the freezer so it makes different shapes once it freezes. This should be ice they have to get through to get the treats, not just a bag of frozen treats. You can also toss in a Nylabone or other toys that can handle being frozen. You can also use a cheap plastic food dish and place a toy or treats in there and freeze. Takes longer for them to get the goodies out since the bowl blocks access to all the sides.
For smaller dogs just add less treats and water.
For small animals use an ice cube tray and toss in a treat or two per cube.
Don't forget just tossing some ice in the water bowl is also entertaining!
This can get messy so please be aware of the fact that ice melts if you have carpets. This is better for floors you can clean easily or outdoors.