When people are fired from their jobs they no longer have money to spend, they don't take that trip to Disneyland this year (or whatever) and that shows up as reduced airline trips and miles driven, which impacts gas prices. Similarly because they're not buying as much consumer stuff that impacts deliveries. Businesses tighten spending which means less B2B stuff being bought which reduces manufacturing demand (and deliveries). That all drops demand for all kinds of energy and petroleum products.
I didn't mention the words "food" or "gas"[*] because I thought it was obvious, this stuff is really, really basic economics. The economy is all connected, so someone's contraction in spending is another market participant's contraction in demand--and as businesses see a contraction in their demand they adjust to contract their own spending.
When it comes to food, people contract their spending by starting to make coffee at home or just buy starbucks less often as a splurge rather than a daily thing, so that contracts revenue for starbucks, that leads to layoffs, which leads to less consumer spending, etc. The prices of staples don't usually drop as much because people still need to eat, but with reduced energy and transportation costs the supermarkets can reduce the cost of milk to try to attract customers.
[*] Actually on re-reading I did mention food and gas: "The reduced demands for goods then filters through the system producing more layoffs and more reduced demands for goods across every sector and the economy contracts into a recession." And "every sector" really means literally every sector of the economy--including "food and gas".
