Okay, the cock ring I have some experience with. The designs are legion, so my best advice would be to try it on some night when you're alone (or afternoon, if she's there every night). Make sure you can figure out how to get it on without fumbling (makes you look more professional) and without hurting yourself.

The one I have MUST be put on while I'm soft. Others don't have that restriction, but you may need a lubricant to get it on while you're hard. Also, some are adjustable, so you can stay hard without cutting off your circulation (only reducing it). Experiment to find how tight you can get it without your penis turning purplish red. If you get it too tight, you can only wear it for 30-60 minutes (depending on just how tight), which defeats your purpose.

If you're trying to keep yourself from cuming, you may be disappointed. My experience is that there is no degree of restriction that will prevent ejaculation, and that the restriction itself hastens arousal. Your experience may differ, of course. I find that, aside from heightening the sensation at orgasm, the primary purpose of a cock ring is to keep me hard after I cum.

Which brings me to the Viagra. In a word, don't. There's a reason it's a prescription only drug. In people with pre-existing heart conditions it can cause a rapid-onset heart attack. Also, most people aren't aware of what the functioning mechanism of Viagra is. It will not help you attain repeated erections. It is not an aphrodisiac. It will not keep you hard indefinitely. It won't make you any bigger. It won't have much (if any) noticable effect on a person who "...does okay on their own". It will take about an hour to have any effect at all.

Seriously, if you want to get it up several times in a night, the best idea is to abstain from sex for 48-72 hours prior to the big weekend, then PACE YOURSELF. Figure that you're going to need an hour (or more -- you would know better than I) soft between each erection and make a plan for activities that don't require your erection (several of them, in fact).

Remember the line from...some damn song or other..."Which do you choose, a hard or soft option?" (East End Boys And West End Girls) If you're going to have two and a half days for this, it can't be bang-bang-bang all of the time. There are also soft options -- things that keep the mood going without requiring a lot of effort or minute-to-minute planning. More like concepts or guiding principles. (I assume you're going to ask for examples. The best I could do for you would be to refer you to a book you'll never be able to find by next weekend: Surrender, by Anonymous, Carroll & Graf Publishers Inc., New York, c.1993, ISBN 0-7867-0035-1)

Of course, your fascinated fellow Forumites will probably have suggestions of their own.