To travel around the world and carry all the essentials is a daunting task. Just answering the question, what is essential? - may propel you into a tizzy. Then, take a deep long breath here, to add souvenirs to your pack, when you need to carry, cart, roll your luggage over rough terrain, up three flights of stairs or on your back, can put you over your limit.
I use one kangaroo suitcase, marketed as the Meridian Osprey. I bought it at REI, San Francisco in the "used" section of the store for $90. It retails around $319. It is the toughest, strongest, heavy duty-est case, I own. Had to get over the ruby red color, and it was worth it. The big lower case houses, two pairs of socks, four shirts, two trousers, my chartreuse raincoat and fleece, one dress up outfit, pajamas, two pairs of shoes and various sundries. Everything must dry overnight. The top part usually houses wires, adapters, travel papers and art supplies. Thats it.
Most times, I become enamored by local artifacts - I buy one, say I'm going to send it, never get around to the post, move it around in my suitcase, and leave it on the bed of a hotel with a note for housekeeping.