Travel can be expensive enough even before any surprise expenses, but the number one most complained about extra cost is actually the easiest one to avoid.
All you need to do is pay attention to the luggage restrictions your airline has in place.
Although you may be lucky enough to get someone flexible and friendly at the check-in counter, don't count on this when you're packing your bag. It's not like the speed limit where there's essentially an accepted grey area.
If the bag is overweight, its overweight - and they have the right to charge you for it.
Some airlines give you a much larger luggage allowance than others, so if there's competition on the route you're planning on booking, it pays to check what sort of allowances are on offer.
As for carry-on luggage, there's pretty much a universal rule of 7kg max.
Due to people trying to sneak through a little bit extra, it's becoming quite common for airlines to weigh carry-on luggage before you board. This can cause a last-minute headache if your bag is over the limit, because you'll need to check it in.
Here's a list of the luggage allowances that apply to some of the most popular airlines out of New Zealand:
All examples are for standard economy fares. They don't include allowances for 'seat only' or premium fare options.