I know most people here are from Clayton but for those who are attending Caulfield:
Not too many food choices. The Monsu Cafe is alright, The Gryph Bar is great in terms of food and atmosphere and runs daily meal specials, Mama Dukes I've heard is alright but no experience in that one. Nice Sushi place ground level near the gym, too. KFC, Gloria Jeans right opposite Caulfield Station, as well as the obvious Coles. There's a Subway too, which is located a 5 minute walk away (across Princess Highway down Waverly Rd).
If the main library is rather full, enter the library area doors and turn immediately to your left and you'll find several rooms full of chairs and desks where you can study. I found these rooms weren't used too much during semester and there's usually always seats available if the main library is full. Main library is good, has some quieter areas on the higher levels so do explore that. Has a large open group area too which is usually a bit louder.
Free weekly BBQ on the main lawn, think it was Wednesdays. Always a big line for lunch!
Main lawn area is a nice place to relax when MONSU provides beanbags or you can just relax on the grass. Otherwise, The Gryph is a decent place or you can head to the (bit small) student lounge second level near the MONSU desk with soft chairs and eating space.
Microwaves located at the student lounge area near Monsu (behind the large red sign/wall). Alternatively, a couple microwaves are located to the left of the main library where those study rooms are.