While I don't specifically do Napoleonic's, I did buy the French Camp Set. I like to have commanders, messengers, and other administrative, mess and supply and maintenance troops.
A 20th Century set could replicate a brigade, regimental, or divisional headquarters. Unit commander, deputy commander, 4 to 6 staff officers, 3 or four messmen, troops with radio, field phone, generator, men with binoculars, scissors scope, men typing at field desks, writing, checking maps, military police.
Tables, chairs, food, cooking units, barrels, supplies, desks, enigma machines, typewriters, radios, speakers, telephones, guard dogs, female administrative soldiers, pets, flags, a soldier with an accordion, violin, guitar, or other musical instrument, and other military bits.
I would buy a number of each for each unit. Certainly all the major WWII and WWI combatants, USA, Soviet Union, Germany and Japan for WWII and France, USA, and Germany for WWI are the ones I would be most interested in.
Since my collection is vast, I would buy them in significant numbers.