1) Back Squat to max in 3 attempts
2) Bench Press to max in 3 attempts
3) Deadlift to max in 3 attempts
Notes: Strongly recommended that you take a good 30 minutes between lifts, eat a snack (sugar is your friend,) watch some Regionals, etc. Treat this as if you were actually going for it in a meet, i.e. make sure your opening lift is a sure thing, second is a very nearly sure thing. Something like 1 @ 7-8, 1 @ 9, 1 @ 10.
Notes: Time trial. Do this 4+ hours and a good meal after your mock powerlifting meet.