Easily available, cheap and calorie dense foods and drinks sold in large package or portion sizes make a huge difference. It's been shown that people have a strong tendency to finish their meals instead of leaving any on the plate regardless of portion size and feeling about equally satisfied. The marketing and sales of such items should be limited somewhat similarly to how some countries limit the sales and marketing of alcohol. Non-walkable communities and a lack of bicycle lanes or paths make a big difference, too. Perhaps it would make sense to put tax incentives in place for employers to provide gym memberships and the like as fringe benefits.
Any low-calorie but nutrient dense foods that the human body has difficulty getting calories out of such as high-fibre fruits should have lower VAT at the expense of unhealthy alternatives. Nutrition information should be provided to the public more readily than it already is.
I 100% agree, there are plenty of easy nudge type policies we could implement really easily!