The bigbox stores sell "stone" spray paint. A can costs between $6 and $12 usually. I like to mask off the edge of my basic snowboard helmet and paint it with this stuff. While I'm at it, I remove the lens and strap from my ski goggles and paint them to match my helmet.
One of these years I'm going to buy or make some foam "gravel" and glue some of that stuff on the helmet.
Enjoy the comments in the lift line since you'll be the only one with a rockhead helmet and matching goggles (well, maybe not now...).
Step 1: Shiny Helmet
Ever wonder why helmets are shiny? Maybe so they'll skid better on asphalt and concrete and keep your neck from snapping?
I'm not too worried about my helmet "grabbing" the snow, but if you paint up your bike or skateboard helmet, you may wish you had left it slick.
Step 2: Prep Time
I don't do anything to the lid for prep. The texture of the paint will hide any scratches anyway. If you think the paint won't stick too well to your lid, then scratch it up with some sandpaper.
Then take a roll of painter's masking tape and cover up the edge of helmet to keep the overspray from getting all over your lining. It helps to stuff the lid with crumbled up newspaper too.
Painting the goggles is a pain. I remove the lens and strap and use small pieces of masking tape to cover the edges and vent fabric and foam where I don't want paint to go. There's no reason why you couldn't paint the strap either - probably would work better to stretch it out a bit and then paint it. At the least, flip the strap over when you put the goggles back together. Logowear sucks.
I generally buy the Rust-Oleum brand but the Krylon or other brands should work just fine. If you don't like the stone look, there's lots of new spray paint in the stores now that are especially made to stick to plastic.