entertaining 5month old

My little one is already moving around quite well (rolling, getting up on all fours and projecting herself forward), holds toys pretty well and is getting bored with same toys. She'll be on the floor by herself and her toys for maybe 10-15 minutes and then she'll be bored and I'll go down to play with her. And I am short of ideas of things to do with her. I sing to her, dance with her , play with toys. She's getting bored of her toys but I don't want to buy things . Ideas??