Tip from someone who works in a school - if you get Wall-E or Dr Who or anything else popular, put a strip of bright tape on it, or hang a keyring from the strap - anything so your child can identify their Wall-E lunchbox from 10 others on the trolley.
this site has loads of types. I found that the zip-up, insulated types are the best. (Although I had to stop freezing the juice cartons as they weren't actually defrosting!)
I generally do; sandwich or wrap, one or two types of fruit cut up, a yogurt, carton of juice plus sometimes a fairy cake or a cookie. Ds also likes cold sausages, cucumber/carrot and hoummus, crackers and cheese. I always give him more than he would eat at home and he always eats it all to my amazement!
We sometimes cook extra tea and use leftovers for lunch bags, like chicken in breadcrumbs or veg pasta. You can also buy insulated pots like a vacuum flask but a pot that you can put hot food or soup in, I haven't got round to getting one yet though!