That is such a wide open question hard to answer. Is the food product a specialty product or mass market? Is the product one of 100 other entrants or unique in its ability to establish a new category/sub-category? Who is the market? These and many more really impact the answer.
In general my experience for a new product, especially if in a crowded category, is that some level of sales must be established before you can approach any sizable chain, broker or distributor. Not always, but usually. That means you beating the pavement and pitching to small privately held retail stores to get shelf space, whether that is at POS, an end cap or front facing shelf space. It is very tough to go directly to 100 mph without building sales store by store when starting out.
In terms of advertising focus on the display/packaging to be the ad vehicle, backed up by smart use of social media. You won't be able to cost effectively "advertise" in the beginning, it is very expensive. On top of that even just paying slotting costs in traditional retail can be very expensive. Not to mention that you have to figure into the cost of the product other expenses like coop marketing dollars and retailer incentives. These costs are why the markup on many items is very high - the cost of actually getting to a sale is very expensive.
If you don't have a background in food, food distribution, or channel sales I would recommend you get some pro-bono advice from others that can take a close look at what you have. People in this industry usually will help if approached correctly, or at least that has been my experience.