The simplest thing to do is to make a list of what you can buy in your local shops, which will be different to what I can get, and then look them in the Tortoise Table Plant Database
In an ideal world, you only buy organic. However, that is not within everyone's budget. My take on it is that if the plant is grown for human consumption then the fertilisers and pesticides used will be safe for your tortoise. Always wash everything before you feed it though.