Advice about gardening in cooler climates?

I live in Tahoe, and the summer days are very warm but it's not unusual for nighttime temperatures to drop into the 30s. Currently in my greenhouse I have romaine and erhead lettuce, spinach, heirloom tomatoes, squash, bell peppers, jalapenos and green chiles, broccoli and cuber. It's getting a little crowded. Which, if any, of these veggies would be fine outside of the greenhouse and be able to survive the chilly nighttime?