As schoolchauffeur says, a hug, a helping hand.
After 15 years of picking up your shoes and cooking your meals your mum will really appreciate small jobs being done without asking.
The other thing which would be wonderful would be if my 11 and 15 yo could read a clock.
They're not bad for school in the morning, but going anywhere else I have to nag.
If your due to leave for a piano lesson, hockey, friends house at 6pm, please be changed with your, music, PE bag, money, phone etc at 5.55pm without having to be reminded 3 times.
The taxi service I'm happy to provide, it's having to stop what I'm doing to sort out the passengers that tribes me mad.
By almost 12 DD2 can manage, phone, money, coat, clothes and shoes suitable for the weather and whatever kit is needed.
I say can manage that doesn't mean she or her 15 yo sister do!
I think more than anything as well as loving words and hugs, we like to see our teenagers doing some of their own thinking.