https://www.amazon.com/gp/product/B00BKVPU08
These things are amazing. You can buy them at menards, or other hardware stores as well.
I got a s biner lock for my Fanny pack!! here on Amazon
I use small nite ize lockable carabiners on my GR2 40L as a deterrent Nite Ize S-Biner MicroLock, Locking Key Holder, Stainless-Steel, Black https://www.amazon.com/dp/B00BKVPU08/ref=cm_sw_r_wa_apa_i_llhMFbPXB4BG8
I got this lock for my Fanny pack! Even I have a hard time opening it so it seems impossible for someone else to. s biner micro lock