What to actually pack?

This is my first post here, as I will start traveling in about a month.

I‘ve been doing a lot of short trips last year, so I know what to pack for 3-5 days, but now I will leave for at least 5 months.

With this in mind, I feel like I just pack the same things as usual, but more clothes.

Am I missing anything?

A trolly/backpack + hand package should be enough, right?

Edit: a South-East Asia trip, including Singapore and Koh Samui.