You can't sacrifice a Junk token to pay multiple costs. For example, you can't sacrifice a Junk token to activate its own ability and also to activate the second ability of Junk Jet.
Junk Jet
If a creature's power is less than 0 when it's doubled, instead that creature gets -X/-0, where X is how much less than 0 its power is. For example, suppose you control Infesting Radroach, a 2/2 creature. If an effect has given Infesting Radroach -4/-0 so that it's a -2/2 creature, doubling its power gives it -2/-0, and it becomes a -4/2 creature.
If you "double" a creature's power more than once in a turn, each doubling effect applies independently. For example, suppose Junk Jet is attached to Infesting Radroach, a 2/2 creature. If you activate Junk Jet's second ability, Infesting Radroach will get +2/+0 when that ability resolves, making it a 4/2 creature. Doubling its power again will give it +4/+0, making it an 8/2 creature.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Billy Christian
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
