I love split stays (we started out doing a 2 resort split between Poly and BC and it's evolved to the point that we have an upcoming 7 resort split - yes we are nuts - over 14 nights - but keep in mind that we've already stayed at most of these resorts on previous trips).
We've sort of learned to live out of our suitcases while on vacation, so packing and unpacking isn't that big of a deal to us.
Like the previous poster, we use an over the door toiletry bag. We're a family of 4 (father, wife, son, daugther) and we pack 2 suitcases, one for the males and one for the females. We have 3 laundry bags (1 for whites, and 2 for colors). Once we start to run out of clean clothes, we do a wash.
At WDW we are always car-less so, for transfers, we either use bell services to move our luggage betwen resorts (for example, if we're going to a park) or we take an Uber (and store our bags with bell services at the new resort if our rooms aren't yet ready). When we've used bell services to move our luggage between resorts, we operate under the assumption that we can't count on our bags being at the new resort until 5 pm. So, in that case, we pack swim suits in our day bags (as we usually arrive at the new resort by no later than 3 pm and often want to go to the pool right away).
As others have noted, Disney does not recognize split stays, so, for example, if you book a dining plan, the credits must be used by midnight of the day you check out of that resort (unused dining plan credits will not transfer over to the second resort).
Split stays sound like a pain but we find them to be a net convenience because, given how huge WDW is, they allow us to plan a vacation where our resort is always close to whatever park we plan to visit on a particular day. The same goes for our ADRs. In addition, we get to experience more than one resort, which, for us is a lot of fun.