As others have said home made sandwiches are always a good bet that way you can make them exactly as you like them. I'm not a fan of salad so shop bought is always limited for me since the majority of them contain mostly salad. Plus you can choose your range of bread or rolls or whatever to suit and it is usually cheaper to get them either from the supermarket or from a bakers direct.
Same with your fillings you can be as creative as you like or as healthy/unhealthy as you want them to be making your own gives you a lot more scope to work with.
Again if you have facilties for heating food as people have said either make a bit more the night before and take it in the next day or batch cook. I used to take in soups in the winter (either home made or tinned as I'm a sucker for Heinz tomato that is my tinned soup weakness).
Even things like home made, pasta, cous cous or rice salads could be an option, again just put in what you fancy your own mix of herbs, spices whatever and your sorted.
I would occasionally buy lunch out as a treat but preferred to take my own as it was a lot cheaper and to be honest I didn't want to waste half my lunch break queuing in one of the takeaways to rush back to then try and gulp it down quickly before going back to work. Plus the fact that my old office was full of boys who did go out pig out on the nearby takeaways was also an offputting factor. My main treats were for birthday/leaving lunches etc when something was organised and we went out as a group for lunch.
I know one was spending about £30 a week on their takeaway lunches and that was before buying any additional things like drinks etc so a large chunk of money to lose for no real reason.