A cheap alternative bag that fits the OE side cases.

[Grumpy]

My wife got this bag of Amazon and it seems to be a near perfect fit for the side case, at a fraction of the cost of the Yamaha ones I have.
No shoulder strap but the material, zips and stiching seem very strong and it folds away to near pocket size.
(I have no affiliation with this product or manufacturer)
https://smile.amazon.co.uk/gp/product/B075R7R4GS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

 

[Kyle_E]

Good idea.

For the US people I found the same size ones ($6 or $9 depending on color)
https://www.amazon.com/Travel-Foldable-Portable-Duffel-Women/dp/B07TG148FM?th=1

 

[Cycledude]

Those bags do look like they should work nice.
I’m using a old duffel bag left over from my trucking days, it’s about 40 years old and looks pretty rough but it still works fine. Walmart usually has a decent selection as well.

 

[Checkswrecks]

Used to use nice expensive ones but found that they'd all chafe through at some point so I've been using fabric grocery bags for years. If the tops of your boxes leak I guess you could put a black trash bag over this.

 

[regder]

Used to use nice expensive ones but found that they'd all chafe through at some point so I've been using fabric grocery bags for years. If the tops of your boxes leak I guess you could put a black trash bag over this.

If you don't mind the aesthetic, I love the blue Ikea bags. Waterproof, indestructible, and fifty cents or so.

 

[ballisticexchris]

Packing cubes are the do all end all!! Various sizes and mesh to waterproof options available. Very cheap. I use the mesh zip up ones found on Amazon’s choice.