1) You are already carrying a powerful piece of demo equipment: your phone. Have a demo setup that you can connect to. If you can afford it, have at least one of those cameras be a PTZ and one be a pano. Then either ask the customer if you can connect to their Wifi, or pray they've got good 4G.
2) Obviously, your process will be different if your prospect is hot, warm, or cold, but here's a few general answers I can give. What I suggest is you give them a preliminary quote with just enough hook them, and then explain that you charge for systems design but give an equal rebate if they buy a system from you. If they object at this point, then run the other direction.
If it's a hot prospect, I suggest giving them the roughest of rough drafts, straight up. You're probably going to want to 'forget' to add some crucial component, but this level of kimono-opening builds a bit of trust on the part of the prospect, which may well be reciprocated by a purchase.
If it's a warm prospect, I'd give them a written quote and verbally give them your idea for how the system will function. Written quote should contain a major-parts list, plus accessories, consumables, and labor.
Cold prospects get a written quote with product types instead of a written list ("2MP dome camera" instead of a SKU, for example), along with a vague description of the system, plus an offer to do a paid system design.
Paid system design should include a major-parts list as well as a layout, including probable cable paths. It should also include items not on the major-parts list, such as EMT piping and gooseneck mounts.
3) USBs are awesome but too easy to lose. I'd give a USB with video clips, along with a trifold glossy and a business card.