Just had to chime in about the summer clothes. I got rid of mine because I never needed them here, then when I went home for a visit this summer had to buy all new because everything I brought was way too heavy for 90-100 degrees!
And I've bought Pear's soap from a local market here, but I don't know if you can find it everywhere.
I have no problems at all here finding ammonia, buttermilk or white vinegar. Really, those items shouldn't be an issue for anyone.
I brought over a bunch of deodorants, boxes of tampons, shampoo, etc., because I was convinced I wouldn't be able to find what I wanted here. Ridiculous. I very quickly found the same products, or equivalents or, more often than not, something I even preferred.
Bring anything with sentimental value and things that you can't replace. But the rest of it ... I wouldn't bother.
I disagree here. I can't find ammonia, buttermilk or white vinegar. Also, I bring home as much Secret deodorant as I can afford when I go home, and I still run out and have to use an inferior product until I can get back. Things like baking soda - 50 cents a box compared to 89p for a little can here - also go in the suitcase, along with my chili and taco mixes, and any other non-perishable foods I can't get.
I also bring home anything I can afford and that will fit in my suitcase that will bring me a little piece of home, especially this time of year. I brought an autumn wreath for my door, and I love those Bath and Body Works concentrated room sprays (in autumny or Christmas spices). I found some American candles in TK Maxx last year (apple pie and pumpkin spice) but I haven't seen any this year. You can sometimes find some things around but it's not guaranteed.
Oh, I would second the sheets too. I would really love some flannel sheets for winter, but can't find them either.