Go to Pleasant Rest Graveyard. Near the gate is a bush called "Death Flower Bush". 
Harvest the flower from it, and keep it in your Sim's inventory. If you die, that 
Sim will give the flower to the Grim Reaper and be resurrected. Although the flower
will not reappear there again, if your Sim has Level 7 Gardening, they can plant 
the "Unknown Special Seeds" found in the graveyard and some other places that have
a chance to grow as a Death Flower. Note: Having the Green Thumb trait to revive 
the plant may help.