What are the laws regarding buying an item, placing that item with other items and then selling the set as one item?

Patent and trademark exhaustion should allow that.

The business model you have proposed may well not infringe any intellectual property rights. However, you should speak with a patent attorney and a trademark attorney regarding the doctrines of first sale, passing off, and reverse passing off.

You are free to create the package you describe as long as you don't state or imply that the individual items came from you. This is essentially what personal shoppers do for a living. For example, you could match a Ralph Loren suit with a Hermes tie but you couldn't sell the outfit under the name Joe X Couture. You'd need to acknowledge the original trademark on each item and you'll need permission from the marks' owners to use the marks publicly. If you are just doing this occasionally and selling the items you personally have bought to someone else, you don't need the companies' permission. But it you're thinking of doing this as a continuing business, you will probably need a license from each company. Plus, purchasing the items retain is going to get pretty expensive.

When the first sale is made - for example, to you - the owner of IP rights has received his or her payment in full. The IP rights are "exhausted." You, as the new owner, have to right to use the item as you see fit - including packaging it with other items, and selling the combination.

Once you buy something (from an authorized seller) you are free to resell it.