I read the heading and the words had a cascading effect on my life memories. It is true, in your teens, you do not really know what is going to happen and one knows not, what will last a lifetime. Your horizon is lower and nearer, life has yet to teach you lessons, so one thinks of childhood and teens as permanent.
The most established institution in your life are parents (if you are blessed enough, to have them around by teenage). No one really tells you, but they are not permanent and one day, if you live long enough they shall depart.
Siblings are next to permanent. If you are the oldest, then it’s likely that they will outlast you. But somehow, age, children, jobs, distance all conspire. It is a relationship which changes from the teen years. By the time you get to my age, it is not the same. Important of course, but subtle changes have happened due to circumstances.
Spouses and children come later in life, normally after university, which means mid 20 and later. So they are not lifelong either.
Friends are another one. Like siblings, time causes change and so the relationships alter over the decades. Again no lifelong permanence.
So what do you actually keep with you all your life?
A) values...once ingrained, values are difficult to alter, whatever the environment or circumstances.
B) beliefs...some beliefs are unshakeable. They do not change despite all trials.
C) songs...there are some songs which last a lifetime (I have about twenty).
D) books...maybe a few. Most disappear with age. Rarely does a book last a lifetime. I can think of only one for me. And, that is tied up to my belief ie. the Quran. A few have lasted since my early 20s. Lord of the Rings, Great Expectations, Ozymandias (poem) etc (a dozen, perhaps).
E) memories. School, and childhood especially. Memories of people long gone. Also memories which seem insignificant, but are essential in your make up. My memory of sampling jungle-jalebi in childhood remains succinct and powerful - unfortunately, the jungle-jalebi fruit has largely disappeared from Karachi. A time long ago, remembered by the little things left behind.
F) pictures...faded black and white ones and some bleached coloured ones. Eid, Birthday, school, holidays, many who are gone (but remain in pics).
G) preferences...these are surprisingly steady throughout life. Colours, taste of food, preferences for faces (oval, square, mixed) attitude (light hearted, serious, intense). Our comfort zone is in a surprisingly narrow band.
To what end do we carry some things a lifetime? They are our identity, enmeshed in what we are. That’s fine! It shows we are still human and can feel till our end.