Well, the Whitney Portal Store IS a good resupply option. Shoot... if you spent the night on the Whitney summit, you could zip down to the store and back up and over in a day.
If you are ok with the descent down the MR, you could leave most of your gear at Iceberg Lk, get your resupply at the store plus a huge burger, and then get back up at least to Iceberg in the same day. Rather than a second summit, you could head west over Whitney-Russell pass.
All of that could be done on your hiking permit from Sequoia N.P., with no Whitney Zone reservation required. ...In fact, Inyo rules are that you can re-enter using the same permit, even after an overnight off the trail. It's ok as long as you are not "out of the wilderness" for more than 24 hours.
And wag bags aren't that bad. You can get one at the Crabtree R.S. or close by. Just try not to use one on the return trip -- it'd be a very long carry back to the west side!
