In the major train station in the big cities like Taipei, and Kaohsiung, there is a stall which would start selling these bentos as early as 9am.
There are often only 2 variants :
(1) the normal bento - where rice is packed together with different types of meat, e.g. roasted pork, bbq chicken, charsiew, lourou (pork stewed in soya sauce and spices), cabbages, pickled and even a hard boiled egg;
(2) the vegetarian bento - where all the meat dishes are replaced with taufu dishes, and vegetarian mock pseudo meat versions.
All the bentos are already packed when they are being sold, so, you can only choose which variant you want, and not what dishes to go in it. Pricing is reasonable considering the amount of food served, a pack is usually priced at ~NTD50-60.
If you are too rushed for time, and didnt have the chance to stop and buy, no worries. The same bento company would usually still have a pushcart seller, to sell the bentos at the station platforms, after you have entered into the departing platforms. On some trains, there are also pushcarts on the train itself to sell the bentos, so, really, there should be no worry whatsoever should you fail to get one from outside. There simply are various touchpoints available, providing convenience to the commuters to get a bento set!
From the company called `Taiwan Railway Biandang" - this is the outer box, which is in a recyclable cardboard (there are no styrofoam boxes in Taiwan!)
Of course, alternatively, before entering the station itself, some 7-Eleven stores also sell bentos set (from another company), and here, you probably could have some choices albeit limited. Mainly it will be on the size of the bentos (small or big), and the type of meats (4 types vs 5 types). All others remain the same, ie it is a prepacked that won't be opened up for customers to choose, but you choose via a printed menu of which set you prefer.
All the bentos will come with a pair of disposable chopsticks, so that its very easy and convenient for the buyer to consume the food bought.
Normally, commuters in Taiwan who are travelling around mid morning, would usually just buy a bento to bring onboard the train, and have their lunch on the train itself! Unlike some other rail services in other countries, eating on board the train is acceptable and very much practised in Taiwan.
Other variants of bento set!