The problem with this question is that it is treating countries as cultures. Besides the problem with subcultures, there are actually many different cultures (understood as languages/ethnic groups/anthropological practices, etc.). This is also not to mention the city vs. village life issue.
If you are talking about traditional life, you will, at least in the lowlands and valleys, a similar wet-rice production culture. If you go up into the mountains, there are different people/languages/culture. There is a lot of diversity in these countries in terms of people (and cultures).One main difference "in general" would be that Laos is more conservative/traditional than Thailand. An example is how in Vientiane, the capital city, Lao women usually wear the "sin" which is a traditional long skirt. You will see the general working people wearing this daily. In Chiang Mai, the traditional "Lanna" clothes are only worn on Fridays (in schools), and by some working people not at all (or only in the Tourism industry).