Here's a simple system: limit yourself to two neutrals - one dark, one light - and one colour (two if you're away for a week or more). *see below for your seasonal colour suggestions
Make sure you have an outfit for each type of occasion: Casual, Smart, and Dressy. Remember, some items will work in two categories eg well-cut trousers (Smart and Dressy) as long as you have the right accessories to zhoozh it up.
Think of your time away as a pie and consider how big each slice needs to be. Is your trip 1/2 Casual, 1/4 Smart, 1/4 Dressy? Then pack accordingly.
Layers are the most practical solution when travelling to different climates. Opt for light, breathable fabrics such as merino wool, silk, or rayon and choose items that are multi-use eg camisoles which can be worn alone or under tops.
Large scarves are easy to pack and wonderfully versatile: sarong skirts & dresses, shawls & shrugs, they covers arms and/or heads as well as providing an extra layer.
Wear your Smart jacket to travel in; it will arrive less wrinkled than in your bag and maybe you'll be up-graded!
Travel Capsule Suggestions
Winters: black and white with bright turquoise
Summers: charcoal and white with smoky, medium blue
Autumns: chocolate and oyster white with muted green turquoise
Springs: camel and ivory with bright aqua
Summers: charcoal and white with smoky, medium blue
Autumns: chocolate and oyster white with muted green turquoise
Springs: camel and ivory with bright aqua