I’ve used that black cat shipping service (Japan also has it) scattered around Taiwan. Cheap and will move your stuff efficiently. I think I paid $300NTD for one suitcase if I remember correctly. Their website is not in English though
https://www.t-cat.com.tw/
Another even cheaper option and less hassle for a backpack is to mail it. I’m not even kidding. I mailed a suitcase to myself once and it arrived the next day. You don’t even need to box it, literally they slap a mailing tag on it and away it goes.
Im pretty sure 711 has an arrangement with a shipping company but I’ve never tried it.