when you go to Europe and ofcrouse with just a carry on you would have to buy some toiletries there. But what do you do when your trip is over and you have normal size liquid bottles and not the 3 ounce how do you get them back with you without checking a bag. ?
You can't take them on board in your carry-on so leave them behind at your hotel for the chambermaid (who no doubt is seriously concerned about sunscreen availability, among other life and death matters.) Buy the smallest sizes you can and then cease worrying about the expense.
... or if you REALLY want the products, go ahead and check your bag on the return trip. If your bag gets delayed on the trip home, you probably have other clothes in the closet and can wait for the airline to send your suitcase to your home. (But if the airline charges for checked baggage, leave the bottles behind.)
To echo Elle's comments, you may not need as much as you think. Try experimenting at home before you leave. I personally survive 3 weeks in Europe with less than 3 ounces of shampoo, liquid soap, hair conditioner, and sunscreen. Occasionally I use the hotel soap/shampoo but it often aggravates my sensitive skin. I have only ever had to purchase one toiletry overseas (sunscreen in Italy - $20 for the bottle!). If you are concerned about bringing them back, take a packable tote with you to use as your return carry on and check your bag (with dirty clothes and extra toiletries) on the way home.
Regarding sunscreen, you can buy moisturizer with sunscreen in it, so no need for 2 separate products. You can also buy sunscreen in a stick form, like deodorant. You don't need to include that in your 3-1-1 bag. Sunscreen is expensive in Europe!
Back in the day, before the liquids ban and 3-1-1, I used to intentionally buy large sizes of European products I really like, to bring home. German toothpaste, Wella shampoo ( yes you can buy itis the US but the formula is different) and Coop laundry gel for hand washables.