Thank them next time
The next time you meet is another chance to say thanks.
Someone takes you to dinner or goes out of their way to help you. You thank them that night. When you see them again, mention it: "Thanks again for dinner. That fish was so good."
Japanese people do this all the time, friends included. It shows you remember what they did. Helping you book something or introducing you to someone can be worth mentioning just as much as paying for your food. A quick sentence when you next meet is enough.