So it may come down to whether or not you can count in having time during the wedding shoot to muck about with tubes, or not. After all...time is money.
Neuro is right with mucking about. I have a 50/2.5 macro with lifesize converter, a 250D closeup lens and an EF25mm extension tube.
I would not recommend tubes for what you want. The process would be:
- remove existing lens
- attach tube
- attach lens to front of tube
- take photo
- remove lens
- remove tube
- replace lens
I use the tube on my 200/2.8 when taking photos of flighty subjects.
For most convenience would be the 250D closeup lens. Assuming you are shooting the 85, you simply need to screw it onto the front. This will give you between 1/3 and 1/2 life size, which is fine for wedding rings. This will give you sufficient working distance. The closeup lens could stay in your pocket. Quality of the Canon produce is absolutely fine for your purposes, not "rubbish" as claimed by another poster. I would get one to suit the lens you will use most often and not get a larger (and much more expensive) closeup lens with step-up ring.
Next option would be a dedicated macro lens. The 50/2.5 would be fine for your purpose, even though it only goes down to 1/2 lifesize. Advantages: cheap and relatively small - you want to minimise gear that you carry around.
The 100/2.8 macro is a little more expensive and goes to lifesize, but is much bigger. You then have 50, 85, 100, 135 and 70-200 which is quite a focal length overlap for someone who will need to carry gear around.
I've done a few weddings. The key is to be fleet on your feet and not be encumbered with gear. Hence, my suggestions.