I would take everything you would for a gig (I always have just incase). However, walk in with just your bass, cables and effects. Let them know you've got the rig in the car just incase, there's no negative here it just shows you're prepared and professional.
Get in and set up quickly, greet everyone and be polite but professional. Make sure they know you're enjoying yourself, don't be the only still person in the room. Confidence sells.
At the end, if you want the gig ask any questions you need answered and only stick around for as long as you feel welcome. If they want you to stick around it's a good sign, remember to get any contact details when you can