You're right about the "drugstore".
We have a "what if" gallon size zip lock bag with such items. We didn't catch colds or flu the first few times we were on a river cruise, and always figured we could go to a local pharmacy. This can be expensive, and inconvenient to others if the PD takes us to a place "on the way back to the hotel", as we experienced. Then we went from never getting sick, to getting a cold early on. So we tried to figure out how to lessen what we take. We went from carrying bottles of cough medicine, kaopectate, etc, to buying gel capsules. This eliminated a lot of bulk and weight. There's expectorant, congestion and cough medicines all in tablets or gel caps. I have to carry a separate bag of foam pads and bandages for my feet to to pad them daily so I can walk; these are not so weighty. I buy the smallest tube of anti-itch cremes or put in a very small cosmetic sample jar. . I carry about 10 packs of those sewing kits that we get in hotels/ships; I take the packaging off, and put in a small zip bag, plus several packages of nosebleed remedies because I don't know when I will have one. I carry one post-it pad, and a very small stapler and scissors., and mostly I use them a few times to assemble all the papers we get. My "what if" bag now weighs a lot less. I have to say my husband's "what if" bag is a lot bigger than mine, his choice.
We also take travel size body cream (gold bond type) then can discard after used up. Provided lotions give us rashes, so we use our own. Instead of my usual cosmetics, I rely on samples, smaller brushes, pencils, and I transfer face creams into a smaller sample type container and if necessary, carry two. I carry 3-4 sample floss from the dentist so discard as they empty. I was lucky to purchase a 70 spf sun screen with a travel size attached to it; was a handy purchase. I don't like provided shampoo, so I transfer my shampoos in reusable hotel bottles. All of these are not all in our "what if" bag, but are part of toiletry bags. I have scaled down the size of that, too by using smaller bottles and discard along the way as things are used. If I don't use an item in 3 trips, I don't take that item again.
We do not count the weight of our prescription medicine, creams, etc., since we hand carry these. I carry only a small amount of allergy, cough capsules on the plane, so to avoid declaring these type meds.
Since we started using the provided body/shampoo to wash out things, I carry less laundry soap or none, but I do carry some clothes pins. We carry at least 6 hangers for wet clothes if we wash, since most closets do not have the lift off hangers. Then at the end, we throw away the hangers or leave in the closet. On the river ships they use these wire hanges to send your clothes back to your room if you have the crew do laundry. The heaviest item is a travel iron; comes handy on the river ship but on land tours, we found hotels provide irons or pressers in the room.
Our kids laugh at us at the time I take to prepare to pack, but I don't like heavy suitcases and can keep it well within the 50 lb limit.