M.S.
Around when my son was 9mos, he was sitting well by himself (he no longer toppled over) and we added a new theme to each day. For example, Thursdays were pots & pans day, so we got out all the pots/pans/spoons/spatulas and did various things (banging, bubbles, pretending to stir & eat, putting toys under one and trying to find it, etc). Its definitely all about playing/singing/interacting, as the others have said.
For food, I loved the Baby Blender book - at the time, it got much better reviews than other homemade baby food books, and I loooooved the recipes/ideas in it (she had a quinoa casserole type thing that was a big hit and something that I wouldn't have thought of at the time).
Good luck!