Well you sound like you're doing better than many people, if it looks tidy superficially. Also, that's what buyers will see: yep they may look in the odd cupboard, but i dont think they'll judge you harshly for the odd drawer-of-crap. We all have those!
But I understand how depressing that hidden clutter can be, and it sounds like you're on the edge of it overspilling into not-enough-storage-to-keep-it-all-hidden. Fortunately, you can choose to do it little by little, one cupboard at a time, and it won't wreak havoc on the house in general.
Let's talk towels... Do you need a place to store towels? Of course you do. Is the current repository the right place? maybe not. Think about where you'd choose to store them if you were arranging the house for the first time, and keep an open mind to a potential domino effect of rearranging... You can't keep the towels in the wrong place forever just because there's something else wrong in the towel place. Now, how many towels do you really need to store, and how many are you trying to store? Cull the rest of them. You might want to downgrade one to dog towel, to be stored with dog stuff, some might go to charity shop, or cut up and edges bound for cleaning cloths. But if you haven't used it for two years, and you're just keeping it for some sort of undefined towel emergency, now is the time to get rid of it. Once you have the right number of towels, give them a bonus wash if necessary, fold them and put them in the towel place, emptying whatever's in the way into a box for sorting next and then reforming to a more appropriate place.
Food, toiletries and cleaning products are wonderful fun to declutter. Pull everything out of each cupboard/fridge. Do you know what it is? Is it in date? Does it look nice (hasn't gone sludgy, mouldy, otherwise unappealing)? Are you likely to use it this year? If the answer to ANY ONE of these questions is no, then just bin it. (I'm not talking about the cheese that's one day over but you were about to use... That's fine. I'm talking about the miso paste that expired circa 1992... YOU ARE NEVER GOING TO USE IT!)
Clothes and toys often provide rich pickings. Does it fit? Is it age appropriate? Is it in good condition? Do I have anything else like it? When did I last use it? If you haven't worn it in two years, it has no place in your life. I know some people stash clothes that they're going to diet into... I think they're just excuses for not living in the here-and-now, but if you must, then at least box them up and store somewhere less accessible. don't let the torment you every time you open your wardrobe. Once you've weeded out the albatrosses, use vacuum storage bags for out-of-season stuff, and for clothes you're saving for your younger daughter.
Save the bits-and-bobs drawer for when you're really mentally alert. I've spend many a fruitless hour looking at a collection of unrelated items (fuse wire, nut-crackers, money off vouchers, foreign currency, optical wipes, orphaned keys and elastic bands), completely losing sight of what I'm trying to do. Was I tidying up, or building a tank, A-team style?