Amex doesn't know about VGCs at the grocery store IME.

If you're looking at meeting Amex MSRs then I wouldn't go to Staples or OD/OM for VGCs. I know those are the stores that most frequently have fee-free gift cards so that's attractive. But I think a 1.19% fee for $500 of MSR is likely outweighed by whatever the SUB is, so I'm good with paying the fee at grocery stores.
Do you have a Safeway reward/loyalty account? There is a (IDK if it's targeted?) $10 coupon for a $100+ prepaid gift card available for that program that you can activate on your account, it expires on 6/29. I bought a $500 vgc at Safeway yesterday for $495.95.
I'm actually not familiar with Dollar General, I don't have one nearby. I would read Flyertalk or r/churning to see the ins and outs of doing that, or if other MSers on our thread use DG, maybe they can chime in.