I would like to use Americas individual state flags and the US State Flag design on a product and sell for profit. Is it legal..

Only your own intellectual property attorney can provide you with a "clearance opinion" on whether your plan is lawful. Generally, it is unlawful to buy a product, amend or remove its brand-identifier [the manufacturer's trademark] and then re-sell the product. That is trademark infringement [either passing off or reverse passing off]. IF that's lawful in your case then the next question is whether you may lawfully affix each "flag design" onto the product in light of all the other flag design trademarks already in use to brand the same or similar products. There is no getting around having to hire a trademark attorney to pass judgment on these two threshold, legal questions.

I concur with Attorney Ballard that you would need to consult with an attorney about the specific object you have in mind. I would also add that most, if not all, of the States in the US have very specific laws about the use of their respective State Flags -- i.e., there is not a federal body of law that governs your right to use the image of each State's Flag(s). So, there will be an extensive amount of legal work that will need to be undertaken in order to assess the legal exposure you would have if you move forward with this business plan.

Many states have ownership interests in their flags. You do not state whether you would be using an existing representation of those flags or designing your own representations of those flags. You need to research whether the flags are under copyright or trademark protection. This includes determining when each work was created, whether the copyright is still in force or whether the flags are within the public domain. This is a labor consuming task that you can research. However, the ultimate decision should be made after you have spoken with an IP attorney.