It doesn't matter how one approaches this old topic... there is just one reasonably elegant solution and that is a laptop with internet connectivity.
Everything else is just a hassle (at best) or a big problem (at worst).
Even if the airport has a GA office where you can just hand in a flight plan, you will probably prefer to file it from your home or the hotel the night before.
Especially if it is an IFR one which can get chucked out by Eurocontrol and if this is going to happen you want to find out the day before and not when you are about to go out to the plane.
This is what I have been doing since 2004 and, subject to getting an internet connection, it has always done the job well.
Before that, I used to do it the old way and, with VFR flight plans, quite a high % simply vanished if I used the DOF/ specification on them. On one 4-leg trip down to Spain, 3 of the 4 vanished.