The advantage of these commercial foods is that they are designed by nutritionist and tested to insure a optimal diet. The shelf life of most commercial foods is 6 months. If the feed contains vitamin C, do not use it more then 90 days from the time it was manufactured. Store your feed in a dry area. Be sure feed is not contaminated by mold or mildew.
Treats are fine in moderation and most welcomed by most critters.
Never feed them chocolate as well. Lettuce is dangerous for many species as well. Some wild berries are toxic to certain species as well. Check with your veterinarian. Which brings me to one of the most important issues on keeping your animal healthy.