Running

i think with a pack as big as a 32l you're going to struggle if it it's not full when there's not much you can do to compress it which looking at the omm website seems to be the case.

I remember seeing a guy run past me on saturday and he had a similar situation where his bag was 1/3 full and it was swinging about a foot on either side of his body and looks like the least comfortable thing ever (especially on a 100k race).

is there a stretchy mesh pocket in the bag? if you're not carrying a lot it might be work putting the heavier/bulkier items inside the pocket to keep it as close to your back as possible and not able to bounce around so much....

you could also make your own compression straps quite cheaply and just loop them through whatever anchor points around the bag you can find. I used the daisy chain loops on my salomon vest to do the same with some simple items off amazon.

https://www.amazon.co.uk/gp/product/B0073UN4US/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
https://www.amazon.co.uk/gp/product/B01BVBQM9E/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
https://www.amazon.co.uk/gp/product/B01BVC9TCU/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1