Can I carry this bag on?/Can I take this on board? /Can I hand-carry this?
Ground staff: Yes, that would be fine.
No. You need to check it in.
on board 登机
check （在机场指托运）托运+in, 酒店指寄存行李
L: How many bags would you like to check in? 你有几个包包要托运呢？
D: Um, I've got one bag, but can I carry this on board? 我有一个包包，但是我可以带这个登机吗？
L: Yeah, that would be fine! 可以，没问题！