IF you are purchasing from a dealer, they should provide you a temporary registration for probably 3 business days, so in addition you will probably be covered for the weekend. Also, call your insurance company, give them the VIN and get at least a temporary insurance. Keep the bill of sale in your car and I think you're covered.
IF buying PP and for any other q's, call your local DMV office. Probably avoid speeding too much, because you never know if you get some pissed off cop type who can give you a headache without all the documentation.