What is useful?

I came across an interesting discussion at http://dobbscodetalk.com/index.php?show=One-Million-Years-B.C..html. Here is a summary of it:
“What if one was transported 20,000 years into the past, with nothing but what happens to currently reside in one’s brain. You meet up with the local natives. If you could initially convince them not to roast you for dinner, and get them to accept you into their tribe, what lasting benefit could you bestow upon them based on your knowledge, unaugmented by any technological infrastructure or reference material?
“20,000 years ago, man had fire, pottery, bows and arrows, and clothing. But he didn’t have writing, agriculture, or metals. It’s surprisingly difficult to come up with some knowledge that can be provided that:

• they could understand given no technical knowledge
• would be clearly useful in their lives
• did not require some supporting technology”

There were different suggestions by different people on that could be a good contribution to such a society.
Then I started thinking, what is it that we have that can be useful to such a society of 20,000 years back? There is also another related question. Suppose, instead of 20,000 years back, if I land up 20,000 years into the future, when technology would be so much advanced, would I have anything that I can give them?
After long thinking, I found that moral and spiritual values don’t change across time. “Love thy neighbour”, “Don’t tell lies”, “Contribute more than you consume”, “Seek long term development instead of short term results”, etc are equally applicable in a society 20,000 year back or 20,000 years later. Human societies change. Art forms change. Technology changes. Science does not change, but it is hardly useful without technology based on it. But human values don’t change. Philosophy does not change. Religion does not change. It is the principles of values, philosophy and religion that are as eternal as science and nature, which can be equally useful to any society, however primitive or advanced.