I think it really depends on what she's used to doing. A change of scenery and a chance to interact - both with other people and with things. Opportunites to look, touch (taste!!).
We don't have any other kids, and none of our friends have kids, so I've been working on getting him around other 'littles'. Our local library has monthly (in some cases weekly) storytimes for all different ages - we went to one for 0-24 mos. He was the youngest, and didn't show much interest in the books or games, but at least he got to see other kids. We're going to try it again next month. Our YMCA has a couple mommy & me type things, also... yoga, can't remember what else. I've also heard that at Gymboree you can try a class for free.
When I'm in Walmart, grocery store, etc if I see a baby/little kid, I'll say it loud enough that the parent hears (i.e. "Look, Rilen! There's a baby!!). The parent usually smiles and we introduce the kids to each other and let them look at each other a few minutes, while we chat about ages, etc.
We live in a city neighborhood, with lots of trees and buildings real close together. With the really bad heat, we were mostly staying inside, but lately we'll go out and touch the trees & leaves. Hang out with neighbors who are out on their porches. Maybe see a dog.
I've also noticed that he's really excited by SHINY, right now. We were in the grocery store and he practically jumped out of my arms when he saw a silverware display. Oh, yeah... when we go shopping, I'll find a safe place to park the cart and then carry him around a bit, so he can see/touch things. He's very interested in textures right now... especially if we haven't clipped his nails and he can make a scratching sound on the fabric.
Also, you said she isn't quite sitting up on her own, yet. We have an old used stroller someone gave us, that we keep in the living room. We put the seat in the sitting-up-straight position and used rolled blankets to prop him up. Then we give him a couple toys to occupy him and he'll play like that for a good 20 mins... or until he leans over too far and gets stuck. His sitting has really improved since we started doing that. You could also (if you don't already) start putting her in a high chair while you eat your meals.
Maybe some of this will give you ideas...