i know from experience that you aren't going to make many new friends asking about ripping stuff out of your "luxury sedan"
but to start you can:
edit: the neon kit would be the first place to start
lose the spare/jack/lug wrench (if you feel you have invincible tires/good roads)
remove the trunk interior, back seat, hardware, rear seatbelts, etc
.......carpeting, pillar covers, roof lining, the motorized parts of your sunroof, air conditioning unit, power steering unit, door panels...it depends on how much of an infiniti you want your car to be once you lose the 500lbs
people will hate, but when i'm looking for a driving experience i dont really care if i'm basking in first class leather. if i wanted luxury included in my driving experience, i'd still have my 97 concorde LXi (two giant leather couches pulled by a big V6)