For color on a budget, Fuji Superia 200 is tough to beat. Kodak Portra 400 is even nicer but costs a bit more. For b&w, try Ilford XP2, a c-41(color)process film you develop anywhere that takes your color film. It has huge exposure latitude and can rated anywhere between 100-800 ISO.
Lenses? The Nikon 50/1.8E is sharp, cheap and tiny--all the better to fit your FG-20. For more reach, the Nikon 100/2.8E is a killer portrait lens that goes for far less the 105/2.5 everyone who never shot the 100/2.8 will tell you to get. In wide angles, the 35/2.8 and pricier 35/2 are nice, along with the 28/2.8AIS. Above all, make sure you're buying Ai/AiS/ or Ai-converted lenses. Older, Non-Ai lenses won't fit.
Despite being mint, your new FG-20 may need a new light seal at hinge on the film back. Old foam decays and needs to be replaced--an easy DIY job. I've refurbed a shelf-full of pretty but elderly Nikons and most needed that seal redone to be light-tight.
Sweet little camera. I have an FG that I often have with me in a pocket or bag.