Renting a car for your stay is another big expense where you can shave pennies (and whole dollars) if you're careful. Larger cars may ride better, but they burn more gasoline than economy cars. When considering transportation, it's always a good idea to strike a balance between comfort and economy. If you'll be spending most of your time at the family reunion instead of on the road, is it really a big deal to lose a little leg room in transit?
There are other ways to save, too: If you have insurance coverage as a perk with one of your credit cards, be sure to use that card to pay for your car rental and refuse the coverage offered by the rental company. Check your credit cards to see what perks you're entitled to, and read the fine print to familiarize yourself with the details. Some policies exclude mini-vans, for instance, or have higher deductibles than you may be comfortable with.
If you'll be moving from destination to destination and plan on dropping the rental off in a different city, state or country, you could end up paying big for the privilege. It may be cheaper to rent and return a vehicle at each destination. It's an added hassle, but could make money sense if the alternative means skipping meals or staying in a hotel with fewer amenities.