What you need is silicone gease.
Specially since baby powder may not be an option depending on the color of your jacket.
There are several products and very low cost alternatives that can be used "off label" for his purpose.
Thermal paste for your overclocked gaming rig: nothing but silicone grease.
Seen that greasy thing they use for soldering? Soldering flux is the some same stuff as the CPU thermal paste: silicon grease. Borrow some from school's electronics lab. (You may find yourself suddenly very popular among the electronics enthusiast crowd, though ;) )
Most pastes are odorless, although you can find scented and even flavored! alternatives at your local mall's sex shop, where they sell the stuff as Silicon based lubricant (it's the non-water based lubricant that won't dissolve condoms) this is a good investment, I doubt any of it will go to waste.
Also, you can find the stuff as "Rubber seal lubricant" at the hardware store. Comes in two varieties: automotive (for door/window/sunroof rubber seals ) or residential: ( lubricant for rubber door seals).
A blob the roughly the size of a cashew should be more than plenty for coating the most squeaky parts of your jacket, and then some.
Slicon grease won't swell, corrode or dissolve your jacket as using petroleum jelly or some other Vaseline based ointments will do.
WD-40 would do the trick too as one of it's many uses is as a rubber lubricant, but odor may be an issue.