I've talked up the importance of digital luggage scales before, but the biggest disadvantage has been trying to track them down at a reasonable price. Not any more.
The pictured Balanzza scale — a successor to the one I wrote about last year — can be had in your local Officeworks for $26.98. (I imagine you can probably find it in other retailers as well, but Officeworks is pretty ubiquitous.) Even if you're not pursuing a Hand Luggage Only-style project in the future, it's a good way to avoid unexpected excess baggage charges.