The Past Rusty (or Good Rusty) is the alternate timeline version of Rusty which he did not become a Pokemon Master, but opted to become a deli chef for the rest of his life by the behest of his Future Counterpart.
As Past Rusty goes to deliver the Chicken Panini to Professor Tree (while singing the theme song), he was interrupted by his Future self coming out from the portal. As Past Rusty asks if he had become a Pokemon Master, Future Rusty opted him to become a deli instead, which Past Rusty agrees.
During the Bidocalypse, Past Rusty and his parents did not become slaves due to Beige Town not being on the map, and they work as usual. Before the Anti-Bidoof Resistance's victory, Battlebart ordered a Party Platter set before Peanut Butter eventually found their base and nearly slaughtered the members.
As Past Rusty arrives to the base to deliver the order, He meets Future Rusty again, asking if he has fulfilled his destiny, and much to his annoyance, Future Rusty tells him to go away. Peanut Butter also smells a delicious aroma on his bag, and Past Rusty reveals that this was his "Rusty Special", his own Sandwich recipe. As Peanut Butter ate the whole sandwich, he finally develops compassion & restored his faith in humanity due to the simple yet elegant ingredients, and he thanked him for realizing there is hope buried inside even the worst of humanity (which had made Future Rusty calls his past self as one, even though that this was all of his doing). Peanut Butter offered Past Rusty to go on a journey with him (and with Cleffaye Valantine).
As Past Rusty was gone with Peanut Butter & Cleffaye, Future Rusty took his place as a deli cook.