You can put almost anything you want in a balikbayan box as long as long as it's not something that's illegal and it's not perishable. Just make sure that the whole surface of the box is completely covered in strong parcel tape and with at least two or three layers of tape on it if you can afford it. The real problem is more one of theft than what is or isn't allowed. If it is taped up very securely then it's likely the pilferers will pick on someone elses box.