I know I talk a lot about organic foods and veggies and where I can, I always try and choose the organic option. The main thing I know is that I don't want pesticides in my diet. Unfortunately though, it's not always possible to buy organic. It can be a lot more expensive and also, not always available.
For me, I try and do a lot of my food shopping at Unicorn Grocery in Chorlton, Manchester. They have a really wide range of organic produce and it's also a co-op so I feel like I'm helping local businesses at the same time! (There are also Vegetable boxes that can be delivered to your door such as Abel and Cole and Riverford)
On saying that, I don't always make it to Unicorn and I don't always have the option to buy organic so here is what I do, I live by 'The Dirty Dozen' and 'The Clean Fifteen'.
The dirty dozen is a list of foods (I believe change yearly) that have the highest amount of contamination of pesticides. These are the ones I try to avoid buying non-organic. Then, the clean fifteen are 15 veggies that have the least amount of contamination. These I buy non-organic but always ensure to peel them in any case...
According to davidsuzuki.org, the following are lists of the 'Dirty Dozen' and the 'Clean Fifteen'