When I was a kid, sometimes my teachers would have us see how many words we could make from C h r i s t m a s. Examples would be rats, is, cat, etc.
If a word has more than one "h," you can't use it. It could have two S's, however, because Christmas has 2 S's. See? No proper nouns can be used: names, cities, etc.
I'll go first:
mats