Sims can accumulate lifetime happiness points which can be redeemed for lifetime rewards. Players can help their Sims gain points by fulfilling wishes and keeping them happy. If a Sim's mood is in the top section of the bar, they will automatically generate lifetime happiness points.
Also with the testingcheatsenabled true cheat, holding down control and clicking on the blank area next to the amount of lifetime points the Sim currently has will generate more points (500 per click). The cheat must be turned on at the main menu.
A gardening sim can accumulate a lot of happiness points fast as explained in this guide.
Lifetime wish Edit
A Sim must chose a Lifetime wish when growing from Teen to Young Adult, or when they are a Child or Teen and excel at a certain skill. The wish they choose must have something in common with the traits the Sim has, (i.e. if the Sim has the Good trait then they most likely will not have the option of Master Thief for their Lifetime Wish unless customized).