Way to customize the backup file using time machine?

Probably going to trade my iMac in towards a new Macbook. I currently have it backing up to an external hard drive, but I really don't want everything to get transferred over. My main worries are everything in Photos and my music and excel, word, and PP.

I've seen on here to use migration assistant, but when I opened that up, looks like the only way that would help is if I bought the new Macbook before trading the iMac in.