Just an FYI, the movies at the campground are for all WDW resort guests, not just FW guests. I haven't ever seen anyone check IDs at resort pools, but maybe some of the more popular spots do check them especially during peak periods. (I wish they'd let FW guests hop over to the WL because FW doesn't have a nice pool, IMO)
As for refillable mugs, I was just there a couple weeks ago (at POR) and used my old mugs. Nothing said. I have reused my FW mugs too and never had a problem. The mugs cost more than at the other resorts for some reason, but only by a dollar or two. I guess they figure that the FW people stay longer than at the other resorts....