If I have my receipt stating that my green card renewal application is in progress, can I still travel ouside the U.S?

Yes, as you are a permanent resident until it is revoked or relinquished. I would travel with that and other evidence of your ties to the US. Have you been outside the US for more than 6 months?

And if you anticipate extended travel outside the US, apply for a re-entry permit while you are physically present in the US. Remember, you must be here for the biometrics as well, usually 30-45 days after filing. Good luck.