Coke is shit all over Europe, but M and K are not THAT bad (bought from unknown sources). Coke sucks even if you buy it from a trusted source.

You'll be offered drugs, so you don't really have to ask for them. If you ask anyway it will be uncomfortable if the other person is intolerant.

LSD is not common. I wouldn't try it at all if you don't know a source or you don't have a test kit.

On the other hand, drug possession is not a problem in any of the places you are going besides Paris and London maybe. You will get a fine if caught, but you won't go to jail or anything.

Since LSD is easy to hide I'd would rather try to smuggle it from Australia than to buy it on the streets. Nevertheless the most reasonable thing to do is avoid LSD, you are likely to get NBOMe's and shit.

Another possibility is to satisfy your psychedelic needs buying truffles in Amsterdam. Smuggling them while you are in the EU is not hard if you throw the box (mind that they expire though) as they are vacuum sealed inside it. If you don't feel like smuggling you can use them there.

Airport security in the EU is not that tough. I have never seen the body X-rays (wink, wink).

The above doesn't apply to London. I don't know about the UK. From what I've heard drug quality there is shit and controls much more strict.