General

My girlfriend is well aware I’m into feederism but does not want to shape her own body in any way for me (I don’t want her to either). She enjoys dipping her toes into my fetish to please me, but that’s it. Actually every now and then we do what’s called a “munching day” where I buy a ton of food for us to stuff ourselves with all day. She’s takes the step further and asks for more than usual. She lets me kiss her belly, listen to gurgles, rub her belly, and that’s about it, it’s all incredibly adorable.
Does anyone know of any incredibly passive activities I can do with her that would not permanently change her body, but something that we could bond over that she can enjoy and have fun with? (She has a vomiting phobia)

How about going to a food tasting event (such as a cheese tasting event) where the whole point is to experience the food rather than to have enormous portions? Learn about the food together and enjoy the food in a sensual way?

Perhaps food play or sploshing with something like low cal whipped cream (or even regular whipped cream from a can, it's not so calorific as to be a big deal on occasion), eating it off each other and smearing each other, getting messy?

Bloating with something low calorie but high volume, such as eating a huge amount of watermelon, so you she can be extremely full, sticky and bloated without all the unhealthy food?

Those are all great ideas! We’ve done both except the first, so perhaps that’s something we should do, thanks

I don’t know if you are just about feeding, but too tight clothing can give great gaining illusions!

You might consider padding each other to look fatter.
There are a few threads here on that subject.