Usually when my friends travel to Thailand, they would buy back souvenirs in the form of keychains, fridge magnets, little purses, Tshirt or other handcraft items. Initially it was what I bought for my friends and colleagues as well when I travel.
Later, I started noticing that when my friends travel to Japan and Korea, they tend to buy back little tidbits and snacks. We enjoyed the food more than the souvenirs because as they say, the way to a person’s heart is through his stomach.
Hence, for the last 5 years or so, I started buying more of food items and snacks compared to non editable items. Usually when I am in a rush for time, I would shop at 7 Eleven- just pick the snacks they have, pay for it and pack them up in my luggage back. There have been times when I just made a pit stop at 7 Eleven on my way to the airport. I am especially crazy about their burgers and sandwiches.
However, if it is convenient for you, I would really suggest that you shop for your snacks at large stores such as BigC, Tesco Lotus or Makro. This is especially so if you are buying in large quantities to take back to a lot of people. Sometimes you can find interesting items that you can also buy for yourself such as clothings, shoes, cute toys, etc. The price tags are all clearly displayed so you need not worry about having to ask for the price.
For example, the above are cup and packet noodles sold in Makro which are in bulk. Makro basically sells most of the things in larger quantities. Example I drink Ovaltine 3-in-1 and Trio coffee daily and I am able to buy these items in bulk for a much lower price from Makro
You can consider sharing with other friends or alternatively shop at BigC or Tesco Lotus if you are buying in smaller quantities or would like to have variety in your selection.
When my friends are visiting, they would allocate sometime to spend in BigC to shop for various items as they are buying in bulk to take back to their home country. You can really save when you are buying from there because the price is often cheaper than 7 Eleven or at normal convenience stores.