Lots of alternatives
I saw that timesharegroceries has a $19.95 delivery and stocking fee.
Welk Escondido is a bit isolated. So if you some how made it to the resort but didn't have a car, this grocery service would be a great solution.
Welk Escondido is located about 8-10 miles north of the city of Escondido. If you were to go south on I-15 and get off on El Norte you would have your choice of two nice Von grocery stores within a mile. Also at that point you are perhaps 4 or 5 miles from Costco. Esc. has a lot of nice grocery stores.
If you want to stay closer to Welk there is a convenience store and deli in the Hidden Meadows residential community (look it up on mapquest or alternative sites) and they make great sandwiches and sell groceries, wine, beer and liquor (carry-out). The HM Deli is perhaps 5 miles from Welk (shorter if you cut through the gated Rimrock community).
Traffic in that area is usually low with the exception of some occasional periods during rush hour.