Earlier, I previewed someone else’s etymological thread on these forums, here, and actually got some really great answers. Hopefully, you guys would be able to answer a few my questions. I need a word for an on-the-house giveaway product that comes in conjunction with a purchased product. For example, the portable book lamp that comes with the Snuggie blanket – a complimentary gift, or something. I also need a word that resembles a “compromise” between a person and society; for example, conforming to something just because, if you didn’t, it would be culturally looked down upon. Maybe there are no such words (I’m not looking for an exact pinpoint, but a proximate answer), but this community seems very intelligent and came up with very interesting answers in the previous thread.
Does it have to be one word? “Complimentary gift” seems perfectly adequate for the first question. As for the second, you could use “peer pressure” or “mores”.
I have heard the term “sweetener” used to describe free products before. (Using the definition of “An inducement, typically in the form of money or a concession”)
More is the best I can come up with for the second, but there are a lot of words and terms that might work: custom, norm, tradition
FYI, your question is not one related to “etymology”. Rather, you are just looking for words that mean “x”. Etymology would tell you how they came to mean “x” based on their roots in other languages (or traced back as far in English/Germanic/PIE as possible).
Is there another kind of gift?
And can this be called a gift at all, given that it is obtained only by a purchase?
An insulting one? 
Maybe “item” would be a better term.
Not sure where you are as you’ve not filled in your Location field, but I’ve heard Americans call this a lagniappe.
I doubt if anyone outside Louisiana would understand that word. I’ve never heard of it.
Perhaps “bonus gift” or “bonus item”?
That was a favorite word of humorist S. J. Perelman. In fact it’s the one that immediately came to mind when I read the OP. But I agree that premium is a better word for this purpose.
As for the other word, how about acquiescence or accommodation?
It’s the first word I thought of, and the closest I ever got to Louisiana was Atlanta. I’ve seen the word in the New York Times and the Wall Street Journal, and neither has felt the need to define it, so it can’t be all that obscure.
Here’s the Google Ngram chart for “lagniappe”:
So it was nearly unknown in written English before 1860, quickly grew in use till about 1955, and has dropped somewhat in popularity since then. This is why some of you aren’t familiar with the term. It’s a somewhat old-fashioned literary term (at least outside of Louisiana).
Package deal?
Assimilate?
Acculturate?
Fit-in?
Homogenize?