How should people facing colonization act to avoid cultural and economic subjugation?

Think hard and seriously about which of the two is worse.

Do you want to lose (most of) your culture, adapt the newcomers' way of doing things and have a chance of competing with them economically?

Or do you want to keep your culture, but be completely outclassed economically, and live at the whims of a more numerous and powerful neighbour?

Both ways include a risk of losing both anyway, but the first path looks the safest to me.

A bit as an aside, I don't think distinctive cultural identities is something that's inherently valuable to preserve. Some cultures are backwards, disfunctional or parasitic, and their loss is not worth mourning.