Possible things from the feed store:
Chick starter
Grower
All-flock or Flock Raiser food
Meat bird starter, or Meat bird grower
Game Bird Starter
Turkey starter (unmedicated is fine, I'm not sure whether medicated would be or not.)
Duck starter
Any of those is close enough to a complete feed that they can eat it for weeks at a stretch if needed.
Do not feed them "layer" feed unless they are old enough to lay eggs, because the high calcium level is bad for growing chicks.
If you cannot get any of those feeds, for a few days you can give them a selection of people-food and foods meant for other animals. Try to provide some protein, some starches/grains, and some fruits & vegetables. Make sure they have access to grit (small rocks) to help them grind & digest the food. Always provide plenty of water, and try to avoid large amounts of fat or salt in what you offer them. Give them a variety, and let them pick through to eat the parts the want (some will get wasted.)
Protein possibilities: eggs, meat, fish, bugs, worms, cheese, yoghurt, milk, cooked beans/lentils/chickpeas, cat food, fish food, dog food
Grain/starch possibilities: scratch grains, birdseed, any whole grains (raw or cooked: corn, rice, oats, wheat, etc), bread/crackers/cereal (whole grain is better than white or refined or sugary stuff), cooked potatoes
Fruit and vegetable possibilities: almost anything that is safe for people, plus grass, dandelion, and various other wild things. (Some plants are poisonous, so look up any particular plant if you are unsure.)
