I get prepacked wild rocket that does well as a staple since collard greens are hard to come by in the UK. If you put it in a ziplock sandwich bag it lasts about a week. Butternut squash will last forever and is also a good staple. Just cut off the outer 'crust' where its dried up each day and grate some onto the greens. One normal sized one will do me for almost 2 weeks before i have to either throw it, use it myself or get a new one. Sometimes individual supermarkets will do pre-packs of stuff thats regarded as 'safe'. I occasionally get a pre-mix
'Florrette Duo' bag from morrisons/asda that has wild rocket and lambs lettuce
(also known as corn salad) that he adores. You can get pre-cut carrot sticks, bell pepper sticks and stuff, often in the fresh 'organic veg snacks for kids' bits.
This website is great for safe staple foods, variety foods and no-no foods using a traffic light system:
http://www.beautifuldragons.com/Nutrition.html.
i'd advise going on that site and making a list of the 'green staple' foods, and then a seperate list of the 'black occasional variety' foods. Then i ensure i have 2 of the green staples every week and 1 or 2 of the variety foods. I keep the list in my purse so i always have it to hand when shopping and tick them off the list when i buy them. The next week i'll try and get something i haven't ticked off yet. If im limited on the staple greens list, i can repeat them every week and it doesn't matter but i try not to get the same variety foods every week. Once you've done the whole list you'll have a good idea of what your beardie likes and doesn't like. If he likes a food and eats it with gusto i highlight it in green on the list and if he wont touch it at all i highlight it in red so i know what his favourites are.
(I offer each change in food evey day for a whole week so he has chance to get used to it before i decide if he likes or doesn't like it).
Hige adored Wild Rocket and Lambs Lettuce.
(Since he had been sick i'd given him some organic butternut squash baby food he adored):