What do you do to get them out of that rut?

It seems like when my LO's are bored, if I don't help break the boredom cycle then the rest of the day becomes a huge whine fest due to boredom. They will do great for several weeks or even months but then I think they get bored with their toys, or outgrow some. I want to have other activities on hand, maybe art or baking related to break up the day. Would love to hear some ideas that can be done at home, and don't require too much prep! It's raining here today so going outside isn't an option.