@brooke42 , welcome to the forum.
I understand your desire to camp along the way when possible, it can be a good option especially on the Fisherman's trail. There are quite a few official campsites, they're well equipped - just like NZ. Unfortunately they are often the same price as a hostel bed, or close to.
As you mention, I have heard of people who have approached farmers etc and received permission to camp.
Wild Camping along the coast is strongly discouraged (you're a hiker, you know how it goes: set up late, leave early, leave no trace).
is it wise to use - or be seen to use - a stove anywhere outside a campsite in a country that has experienced such terrible fires recently?
Have you looked at any back-packing forums about the difficulties in taking any kind of cooking stove/gear on a plane, even without fuel?
Does any backpacker nowadays need to use gas canisters? Make or buy a simple alcohol burner if you really have to have a cooker. Methylated spirits is available in hardware stores and often bioethanol too nowadays. But really, unless you are staying at campsites, I'd think again about whether you really need a cooker at all.
My strategy (which may well fall over when others comment!) would be to aim at having a local hot main meal in the middle of the day or evening, depending on availability. And the rest of the time carrying bread, groceries, fruit, yoghurts etc and supplementing with tasty snacks in any cafés or bars that you find in between
Hikers routinely carry camping equipment on planes including cooking Gear, there's no difficulty what so ever. Even in carry-on luggage. No gas cylinders naturally, but that applies to many appliances including ladies curling irons!
The only issues for a hiker are exactly the same as for a pilgrim : Blades and Hiking poles.
From a purely environmental perspective I much prefer an alcohol stove.
However, many campers do still use gas stoves because they are far safer. Some of us carry alcohol stoves, they have their advantages.
Safety is not one of them.
If you tip over an alcohol stove the flame goes everywhere: far more dangerous both to the individual and the environment. Hikers are inherently
very careful of the environment: we live in it!
We do try : as mentioned by
@duncanwhyte refill adapters are available, & refillable gas canisters are becoming more common.
As to snacking in cafes or bars: I appreciate the advice is well intentioned however the OP mentioned his funds are limited.
please, bring your tent because I wouldn’t want to be in the same dormitory as you
Considering that you've several times lately commented that your daily 'budget' is a hundred Euros I think it highly unlikely!
I agree with one point raised by several of you above: the store bought dehydrated meals are prohibitively expensive. Last time I looked a dehydrated meal in Portugal was 9/10 euros.
Personally I pick up cheap meals from the supermarket: there are many, many options, some of which simply require adding boiling water or heating thru, and I can eat well for 3-4 euros. I have to say, I also enjoy the creativeness.
By eating relatively frugally I am then able to splurge on the excellent local restaurant specialities, rather than just the menu del dia.
There is little difference from eating food that requires minimal cooking in an Albergue vs a campsite. There are a few threads that discuss good cheap nutritious food, I recall one in particular this year that had many excellent picnic lunch suggestions. I think some of you participated, perhaps one of us can find it for the OP.