From my Evernote tag for prospective census questions:

On average how many days do you eat meat per week? (Y/N)
Did you eat meat yesterday? (Y/N)

Having those two questions together is a test for self honesty. This is interesting because previous data suggest that moral philosophers do poorly on it.

I would prefer such question above the identity labels of vegetarian/vegan/paleo-eater. I could also be interesting to have it in addition.

Easy wins:
James Miller recently wrote:

Other easy wins: The Squatty Potty, magnesium supplements, meditation, and donating blood if you are male.

I would be interested in questions regarding those factors:

Is the toilet you use at your home the most a Squatty Potty? (Y/N)
Did you donate blood in the last year? (Y/N)

I'm not sure how to word questions for meditation and magnesium supplements. Squatty Potty/blood donations are the most interesting for me.

Better that X guilty men go free than one innocent man be convicted. Solve for X.

When was the last time you read a scientific paper that was work related?
Today
Last Week
Last Month
Last Year
Three Years ago
Longer than three years ago / Never

When was the last time you read a scientific paper that wasn't work related?
Today
Last Week
Last Month
Last Year
Three Years ago
Longer than three years ago / Never

Quantified Self: Have you ever made an effort to record personal data for future analysis and stuck with it for >1 month? (Y/N)

I would again like to have a question measuring spaced repetition usage (I think there was a good one in the 2013 census.