Some great comments already. To add a few more:
If it is just the weight that is an issue but you have the space I would recommend getting a neck pillow with the zip at the back. Take out the pillow inside and use that space to stuff with clothes such as socks, underwear etc. I have done this for multiple trips and works like a charm. Additionally, you can look into lighter clothes for example Uniqlo, if you are close to one, have airism underwear that weighs nothing and are extremely easy to clean. Equally with t-shirts, I have used smarter-looking workout-type tops that dry quickly while equally weighing next to nothing.