I'd had a hysterectomy years before my double mastectomy and had drains then, so I knew what to expect. Drains and emptying them aren't really worth worrying about—they're mostly a nuisance as you'll have lengths of tubing you don't want to catch on anything (some inches of tubing will be inserted under your skin and secured at the opening with a couple of stitches; pulling or yanking on the tubing can hurt if you're not holding onto the tubing either where it's secured, or along its length because of those stitches).

I found a cloth badge lanyard very useful—I wore the lanyard around my neck and using the loops built into the drains and safety pins, pinned my drains to the lanyard so their weight was supported (not dragging down on the tubing) and I could keep track of where they were. I had a couple of lanyards—I'd keep the drains supported with one lanyard while showering and then change to the dry one when dressing.

You will want to faithfully log every time you empty your drains and the amount of fluid collected by each drain—my doctor would only remove the drains when they quit pulling a certain amount of fluid in a 24-hour period. (P.S. I used Super Glue to close the holes when the tubing/drains were removed—reduced seeping and sped up the holes healing.)

You will probably find it more comfortable while resting/sleeping in bed to be propped up and it will be a lot easier to get out of the bed if you're not lying flat. If you are unable to use your arms to push yourself to sit up, a bath towel folded lengthwise (or similar wide strap, or belt) can be placed behind you and your caregiver can grab both ends to pull you towards him/her.

A volunteer support group at my hospital made and gifted crescent-shaped pillows to mastectomy patients; the pillows were similar to the neck/headrest pillows used by travelers to support their heads while napping—but bigger. When resting in bed, the pillow was placed on my chest, but below where my breasts used to be and wrapped around my sides to support my arms.

Try to get your painkiller(s) and other medication prescriptions filled a day, or two before your surgery, so they're on hand when you need them—supply chain problems can make it difficult to get medications and some of these meds (especially opiates) CANNOT be called in; you have to take a paper prescription to the pharmacy.