Hi Sarah
I had the double DIEP last year. There's a long post on this site of what to bring to hospital. Just do a search.
You'll wear the hospital gown for a few days and that's best as they check you so often. Take a pashmina or cardigan or bed jacket to wear over and a dressing gown and slip on slippers for when you want to walk around the corridors. Slip on because you can't bend over!
After a few days I wore yoga pants and loose t shirts. I suggest you bring some singlets like those Supre ones so you can wear them under the binder (it gave me a rash). Granny or full knickers also best as bikini ones will sit on your scar line.
It was nice to have visitors but get them to limit it to one hour max. You'll be tired and may want to have a snooze in the arvo or just read or watch TV.
Skip the makeup! I brought it but it was the last thing you want. Perfume and hand cream nice. You can't shower for a week so I brought big baby wipes to freshen up, but the hospital should have those.
Hope this helps! Oh yes, bring a cloth bag you can put over your shoulder to put all the drains in when you walk around. You'll have 6 to begin with! A shoe or handbag bag would work too. Just need a drawstring.
Good luck. You'll be so happy!
Diane