Airline gifts are really something from the old days, when they were more widespread - so much so that IATA had specific regulations about them (cost, etc).

Certainly up there with the best known are the KLM porcelain houses, so many accounts of collecting the range, there are even collectors societies. They were giving these out back in the 1950s.

The most retained gifts would appear to be the souveniers given out in Concorde.

Wardair, a Canadian charter operator that operated in the 1960s-1980s, always gave out flight bags. They were very well made, a number of people I know who travelled with them 20 or 30 years ago still have one - as I do.