Whether you buy a unique souvenir from a night market in Asia or a designer shirt in Buenos Aires or New York, you'll have to carry the item around in your backpack for the duration of your trip. That may be fine if it's a lightweight and compact item, but our basic advice is to ship home large and heavy items that you do not need while traveling - or, if you MUST carry it around, at least buy it during the last days of your journey.
One of the excitements of traveling the world is visiting and exploring markets of all kinds. Here you will find local artifacts, produce and rarities - and bargaining is widely accepted. There are many rules of conduct when describing the art of bargaining and you should always check for local customs before setting out on a bargaining quest, but as a rule of thumb you should only start bargaining if you are seriously interested in buying. It may be a sport for you to haggle down the price of each and every item (and you are right to do so as the starting price is often 10 times higher than the actual value) - but always smile and accept if you discover that you have been ripped off. You can most likely afford the "loss".
Be aware of counterfeit products such as DVDs, CDs, handbags, clothing and electronics etc. They are usually available in India, China, Thailand, Vietnam and other Asian countries. It's tempting to buy a fake copy which is 10-20 times cheaper than the original brand item, but you can be pretty sure that it will not last as long as the original. You may also encounter legal problems when crossing borders or returning home where customs and local authorities may fine you severely if you are caught with counterfeit products. Also remember that bringing home (or sending) fake items in large quantities with sale in mind is a serious felony which will cost you a fortune and perhaps a prosecution. Don't go there!