Sprung clothespins. You have to take some of the spring out of them or they’ll be too nasty. Don’t get the kind with teeth on the clamp part. Clamp them to a piece of dowel that stretches them just a bit past their normal open point and leave them for a day or so. Try them out on the inside of your arm to see if they’re okay, if not, back to the dowel. You can use them to clamp sensitive spots or use a flogger to snap them off. That hurts, lots. Don’t clamp anything for too long or you could possibly cause damage. No more than 5-10 minutes without checking for blood flow.
Light floggers don’t usually leave long-term marks unless you really put your back into it, which you shouldn’t. Belts give more of a thud and hurt more than sting, but you also have to be more careful in your choice of targets. Thighs and butt are ok, back or stomach, not so much. Paddles work nicely, but like Phase42 said, warm her up first.
What Analogue Skywalker said about oil is worth repeating. Give her a nice oil massage or something beforehand so the wax doesn’t stick to her skin. Don’t even get close to her head or hair. One because it’s dangerous, and the other because wax is hell to get out of hair. Be very careful with open flame around someone who is bound. They can’t flinch away, and if you accidently set something on fire they are very vulnerable. You don’t want to break up with her because you set her hair on fire while she was handcuffed and wearing a ball-gag.
I know this isn’t Bondage 101, but along with all the other safety messages I wrote, I’d be derelict in my duty if I didn’t tell you to have a way of getting her out of whatever you’re doing. Have a safe word. Set up ground rules and expectations. If you’re doing any kind of binding or tying, keep a pair of paramedic’s scissors around so you can get her out of the bindings in seconds should she pass out or have some other kind of emergency.
ALWAYS have a spare set of keys for the handcuffs. Get real cuffs with locking rings so you don’t end up clamping them down on her wrists and causing nerve damage by accident.