It's a little different here in the UK, as things like Lockerbie and the NI 'troubles' forced us to tighten security a little earlier.

Since 9/11, there have been some changes.

The mixing of incoming and outgoing passengers is more tightly controlled (including some ridiculous layouts that mean alternating flows of departing and arriving passengers controlled by security guards with tensabarriers). You have to have all jackets X-rayed on departure. There is also increased screening of incoming passengers.

The few situations where you could use metal cutlery on board were replaced with plastic cutlery (although the glasses weren't, which makes it all seem a bit futile).

Many waste bins have been removed from airport terminals (not helping the litter situation).

Where domestic/ROI and international passengers depart from the same terminal, the domestic passengers have a digital photo taken at the entrance to security, which is associated with their BP (hence no photo ID required for domestic/ROI, even if some airlines do insist on it).

More recently, they've started scanning and recording UK and EU/EEA passports, as opposed to the cursory check (which often didn't even involve opening the passport) in place as recently as a year ago. The queues can be quite nasty as a result (although nothing on the other ones...)

There also appear to be no more no-security flights. There weren't any in the UK (not since Lockerbie), but there were certainly some places in Europe where domestic or prop flights didn't entail any x-ray or metal detector.

Inter-airport transfers were no longer allowed. For example, it used to be the case that you could through-check luggage on LGW-LHR transfers, but this has stopped.

Lounge and gate check-in has all but disappeared here, too. Mind you, that's as much to do with the growth of e-tickets than anything else. But it used to be dead easy to get airside at LHR with an open ticket - I used to keep one of these to help my Gran to the gate.

Thankfully, we didn't continue the 'no carry-on' rule that was enforced for the week or so following 9/11.

I'm sure there's others, and I'm sure the US was far worse affected.