I’ll take some Tree-Of-Life from Known Space and make sure to save the seeds. Further plans are currently indeterminate, my current intelligence is nowhere near human-protector levels so I’ll wait to decide what to do until I’ve fixed that.
Make sure to have some kids first.
Me, I'd say there's a few decent options.
A single bite of Ambrosia can make a human into a full-on Greek God, immortality and all. Removal of injuries and eternal youth are included, along with a portfolio of divine powers. This isn't the very best class of god, they can still be hurt f'rex, but it would suffice. With twelve kilograms I should have enough to bring along a large number of people I care about and create an entire pantheon from my family, friends, and possibly pets, which is fairly appealing. Immortality alone just isn't as good.
I could get more raw power from a Xianxia Qi Elixir. A few drops of the more potent ones grant the equivalent power of years of Cultivation, so twelve kilos would catapult me to the upper levels where gods are mere chew toys. I couldn't bring anybody along in that case, though, I'd need pretty much the entire thing and I'd have to learn how to Cultivate the long way so despite being highest in power, it wouldn't be ideal.
Peaches of Immortality are a viable option. In comparison to the other ideas on the list, they don't grant true immortality or superpowers, just a very extended lifetime (youth and freedom from old injuries included) ranging from +1000 years to +47,000 years of life per peach. Twelve kilograms should be in the area of around one hundred and fifty peaches. These would only be desirable if I can crib Bassoe and plant the seeds, it takes 1000 years for the least effective peach of immortality tree to put forth leaves and then 3000 more years for it's peaches to ripen, with the more effective peaches taking longer. However, a typical peach tree bears between 250 and 300 peaches each crop averaging around 270, so despite the length of time there's plenty of lifespan to go around once they actually bear. With carefull maintenance of the trees I might be able to grant eternal youth to all mankind in sixteen thousand years (I could have two billion trees bearing then) or so.
There's a number of super-serums out there that might be of benefit, f'rex Cahill serum grants the imbiber super strength, genius, cunning, and artistry. However I'd want to research these very carefully to make sure there's no bad side effects, which most super-serums have, and that the effects are permanent rather than needing continuous intake.
Since I don't actually have to order all the same thing I'll probably go with all three options, a hundred or so peaches of immortality, a kilo of ambrosia, and three kilos of elixir of Qi. True immortality and divine power from the ambrosia for myself a couple hundred of my closest friends and family, Qi elixir for myself to ensure I go beyond the limits of mere divinity, and the peaches as a long-term project to help the rest of humanity with me and my other divine companions maintaining the trees initially.
