Exodus 35:3 Do not light a fire in any of your dwellings on the Sabbath day.
When God was speaking to Moses and giving him all the commandment they should follow, he made sure there should be no doubt.
Take this sentence for instance. He commanded them not to light a fire in their dwellings on the Sabbath. He said this so they would not have an excuse to make a quick meal whilst nobody was watching!
God wanted them to rest in Him on the Sabbath. That meant stopping everything and relying on God for a day.
Yes, they could pre-prepare meals and things, but He wanted them to make a point about keeping the Sabbath for Him.
What is He asking you to stop?