Milagro Agave Nectar? I have used this to fill in a few times and it is a good product.

Not sure what I will bring with us this trip, we are checking at least one bag so may bring some cocktail supplies.

On the tart drink page, another that is easy and good is a La Paloma, also just Paloma or in Mexico they also called it a Muppet.
1.5 oz Tequila
1/2 oz fresh lime juice
3 oz or so grapefruit soda (squirt)
Served on the rocks.

My favorite Tequila for this is Antiguo Reposado if you can find it.

This is another refreshing tart drink and simple. Adjust to taste.

Cheers,
Todd