This first item is a postcard, labelled as a "BOOK POST Card", sent from Weston-super-Mare to Cudworth, Yorkshire. It has a "Liable to Letter Rate / 871" cachet because it has a message written rather than just the sender's name and address.
Strictly speaking it is not a postcard because it is the wrong size. From 1st November 1899 until 31st October 1906 the minimum size to qualify for the for a postcard was 3¼" x 2¼". However the card is franked with a 1d stamp, the rate for a letter, rather than with a ½d stamp which was the rate for a postcard, so despite the cachet the postcard was correctly franked.
The envelope below was sent from Yeovil to Calcutta on 4th September 1939, the day after Great Britain and France declared war on Germany following the German invasion of Poland.