Modern Vespa

Not a top case fan but need a little more room to take stuff on a weekend run. Wondering if anyone knows of any decent bag that can be hung from the stock bar/grab rail behind the seat without obscuring the tail light. Thanks in advance.

A general search for handlebar tool bags might give you what you need. Langlitz leathers makes a very nice one, but they don't give it away.

Lots of stuff in the HD and Indian line of bikes.

probably easiest to stick a rack on the battery cover and strap a bag to that.

also read Soft Touring Bags on a GTS

If you're wanting something on the pillion part of the saddle, there's tail bags. I'm fond of either a roll-top duffel or a backpack held on with either Rok straps or a cargo net.

There's mini racks available.

I love the idea and look of the small tail rack and might suit your needs.

As mentioned above, a tail bag might be just what you're looking for. Mounts directly to the seat, so you should be able to access under the seat for refueling, etc, without removing the bag itself.

Revzilla has plenty of options and good videos to help in making an informed decision to best fit your needs.

I have this one. However, I do have a GIVI plate for a GIVI top case. I put the bag on the plate when I do not want the big top case, which is just about all the time.

similar
https://www.aliexpress.com/item/1005002611471976.html?gatewayAdapt=4itemAdapt

Not the bag I travel with on my scoot but Ebay sellers have several weatherized military "gear" bags commonly sold in many sizes. I use a Roadgear scooter bag which has bungees made into it's bottom.