After purchasing all the styles from the 2 style vendors in the Aquacultural area and unlocking everything in your mainframe (backup, orbital, sidekick, supply drop, mods), what else can marks of victory be used on? Edit: I should also add that Constantine was bought out as well as base items.
70 as in cr 70 or something else? vendors accept marks for gear progression well into cr 187 at the start of the 8th tier. i would find it odd if someone said base items are bought out, i'm assuming you mean you no longer have any base items you're after personally. personally i use left over marks from missions to just basically hoard base items boxes hoping i get at least one of a specific item i need.
As the others in here already said: Catalyst Caches (or Episode Crafting Mat if you're into consumables). If you don't need the Catalysts for yourself...a single one sells for 150-300k (even more if a double Nth event is active)
You could start stockpiling role specific affinity mods so you can swap them out like we already have to do for OP gear mods! I'm half joking...half.