It's Rainy Season!
At least in mainland SEA (I am currently BKK based). Don't forget to pack an umbrella that can handle some serious wind gusts and some good rubber soled business appropriate footwear that can handle rain well.
In terms of packing strategy, I would let the luggage allowances be my guide. So be sure to find out which airlines you will ne flying and if checked baggage will be included in your intra-regional flights.
If you decide to replace your checked bag, you may consider a traditional non wheeled suitcase. Such should be able to ride atop your wheeled carry-on. Thus maximizing you luggage weight allotment while reducing the risk of luggage failure.