Most dogs love treats, so learning how to make treats at home can be a cheap and easy way to kill time, a good way to give your results a test run, and make great gifts for other dog owners in the process.
People who endlessly love dogs sometimes like to go overboard, and that's okay as long as the dog enjoys it too. Test the waters first, but if your dog cares little about being in costume, spend some time with them crafting one, trying out each piece as you make them. If they do well, it'll be one more thing you'll have in your arsenal of things to do and one you can show off if the costume ends up humorous or entertaining.
It might not be the most fun sounding activity, but it's most certainly useful for those who crate their dogs or put them in a carrier for traveling. Getting them accustomed to using their crate or carrier when travel or bedtime is not imminent will ease the stress for them if it makes them uncomfortable, as you have the time to do other things afterwards. You can do it in little spurts and get them used to it before the time comes when it's actually a necessity. Most dogs will enjoy getting treats even if they have to work for it, plus you'll likely improve their response to commands and work towards a helpful goal in the process.