RMN is currently 6% at Sam's Club and it specifically includes gift cards.
https://www.retailmenot.com/cashback/restrictions/15477765
If you have the Sam's Club CashApp 5% back and it is a boost instead of a click-through where you must complete the purchase through the CashApp, it sets up a pretty good discount.
Unfortunately, I don't have the 5% CashApp for Sam's Club, I only have 2% back and I need to click through (so you can't also activate RMN cashback).
Sam's Club also limits you to 2 of any gift card type, but if you estimate a 4% discount, along with the CashApp 5% and RMN 6%, you'd potentially net around 13-14% off.
If you can only use RMN and can't combine with CashApp it'd be roughly 8-9% back.