Diaper Bag for 3 Kids?

I have a stupid mom post and I apologize in advance to anyone who doesn't have kids.

What diaper bag works the best for 3 kids? As soon as Baby #3 comes into the world, I'll be carrying significantly more crap with me wherever I go and I'm already maxed out with the current bag. It hangs uncomfortably and when I add to the burden I can't maneuver well to grab hands and wrangle 2 kids, let alone 3 in the parking lot.

Currently I use a Skip Hop Duo bag. It's fine, but I don't see it being big enough for the load I'll need to carry. Here's what I plan to take out on a regular basis (P.S. - my kids are 4, 2 and soon-to-be-born):

-Change of pants/panties for the 4 year old. I haven't needed this before, but I think the one time I leave it at home, I'm sure I'll need it.
-2 diapers for the 2 year old. I bring 2 because one time I brought 1 and the tab ripped off. FML.
-Wipes. Boat loads of them because we use them for face/hand cleaning on the go too.
-Drinks for the 2 and 4 year old (these go in the outside pocket)
-My stuff (keys, wallet, checkbook, phone, etc.)
*blanket
*toys

**my kids have a tendency to ditch whatever object they just HAD to bring with them and then it winds up in the diaper bag.

When baby #3 comes, I'll need to add to that list. I'll be carrying
-3 diapers for the baby for short trips
-wipes
-1 outfit change
-bottles
-formula
-nursing cover (unsure of whether I'll BF or formula feed. BFing hasn't worked out in the past for very long)
-blanket

I'm thinking 2 drinks for the older kids and the formula alone won't fit in the bag. I'm hoping to get my 2 year old on the potty bandwagon soon, but that presents other issues when in public (like dragging 3 young kids into a bathroom).

Has anyone else had this level of anxiety about leaving the house with 3 kids or is it just me? I think we'll be staying home a lot and mostly leaving when dad's around to wrangle at least 1 of the kids. Getting the 3 of them into and out of the car is another experience all together and I must say I'm not really looking forward to this "adventure". Why couldn't we stop at 2?