You said there’s a lake? And fishing? Sounds like a slice of heaven. Ditch the inlaws and fish all day. (Minnesota rules… talking isn’t allowed during serious fishing, and that definately includes witnessing-it scares the fish away).
I step away from my thread for a minute and it dies. 
Thanks again for all your suggestions (funny or otherwise). I am planning on going to Border’s this week to get plenty of reading material.
Thanks again everyone. Yet another reminder of why Dopers rule.
Rob,
Disappear right before you are scheduled to leave. Then on Monday night call up your darling and say: “Don’t pay the ransom, I escaped!” 
I feel your pain. In addition to the books take a small portable TV with you so you can watch the race, games, etc. and leave the main TV to the rest of the unwashed.
Funny thing, relationships. They’re seldom 50-50 like we were promised. Sometimes they’re 60-40, sometimes they’re 30-70. In this case, you’re not happy, your wife isn’t happy; sounds like this is a case where things are more like 70-70!
You’ll probably have to put up with some witnessing, but try to find a way out of it if it gets too heavy. If they usually start at say, 2 PM, then earlier in the day, promise one of the youngsters that you’ll teach him to fish or canoe or swim or row a boat that afternoon, say about 2. He’ll start bugging you about it, and you can use that as an excuse to get out. After all, you CAN’T break a promise to a little kid, can you?
The books and magazines will work for awhile, but if you try to read all 3 days, it’s bound to get you talked about, and your wife will be mad at you for a lot longer than 3 days. Don’t depend on that for the whole weekend.
If you want to bring some videos, try finding a copy of “The Gods Must Be Crazy”. It’s a clean, wholesome, and funny film that the whole family can watch, even the fundies. But the title alone will make them a bit nervous, and you can watch them squirm a bit before they decide it’s OK. You might have to look for this ahead of time, though, as it came out about 1988, and most video stores probably don’t carry it. It’s worth looking for, though!
If nothing else works, go mow the lawn.
That would work if it wasnt on 100+ acres of land, but it would keep me busy.