I agree with @HeddaGarbled and others on P1, that some of this depends on your expectations, and what you are used to.
My parents, for example, only ever had any sort of takeaway (lets be honest - fish and chips) once for a treat on holiday at the sea every year, and if they were moving house or decorating.
Whereas my adult dc consider it normal to have some sort of take away every week.
Right there you have different expectations.
Same with a day out - picnic vs 'We'll buy something there' thinking.
Then your interests. Someone who loves being outdoors, hill walking etc doesn't have a lot of expense beyond petrol to get there. But people who like theme parks or who feel the need to go abroad a lot will have different outgoings.
Some people are interested in life and in people and ready to take up new hobbies, groups, volunteering etc, whereas others choose to keep themselves to themselves and perhaps aren't brave enough to go and try new things - that is going to impact on how happy you end up.
But, I also agree with the posters who are saying that some people are naturally more 'content'. Some people look for the good in everything and set out to enjoy life as it is, whereas others tend to have one eye on what they haven't got. I think this remains the same whatever stage of life you are at. For some people, the peace of not being at anyone's beck and call is what makes their retirement lovely, although it isn't costing anything.