an alien tradition over here - just the "trick & treat" thing

Yes, I agree with that. When I wor a lad, we certainly used to get dressed up (as something scary) and go off and try to scare people. We also used to go for the odd trick such as knocking on doors and running away. But we'd never be "bought off".

An American-style Halloween, including trick-or-treat, Happy Halloween cards , etc only appeared here about 10-15 years ago - which would tie in fairly well with E.T., though I'd never considered that before.

Here's an article from a local magazine, which suggests that trick-or-treating actually originated in Europe (not Ireland), related to early Christianity rather than paganism:

The custom of trick-or-treating is thought to have originated not with the Irish Celts [Samhain etc], but with a ninth-century European custom called 'souling'.
On November 2, All Souls Day, early Christians walked from village to village begging for 'soul cakes' - square pieces of bread with currants
[or caraway-seed cakes, I've read elsewhere]. The more soul-cakes the beggars received, the more prayers they would promise to say on behalf of the dead relatives pf the donors.
At the time, it was believed that the dead remained in limbo for a time after death, and that prayer, even by strangers, could help a soul's passage to heaven.


You can see how failing to pray for dead relatives would be considered likely to bring bad luck, especially at a time when the boundaries between worlds were meant to be thin.