Thanks for all the answers so far.
To clarify: I'm aware of all the fuel reserves and how a planning should be done.
My question is: If it's one of those days (long taxi, i don't get my FL, approach delay, whatever..) and i'm committing myself to my destination (10 Rwys, CAVOK) and I start using my alternate fuel before being on the ground, so I land with Final Reserve, but without Alternate fuel - is this still legal?
Some tell me it's not - I'm looking for the reference if there's one.