It's not clear what you mean by "bulk products" and "smaller products," and you really need your own IP lawyer to disclose to and get advice from.
There have been many similar "repackaging" questions on Avvo:
Basically, you can't re-label something if it's going to still be identifable as someone else's product where your use damages the product, that's called "passing off" and is trademark infringement and/or trade dress infringement, and you can't use someone else's brand to sell your own product. You can however, buy a generic, not identiable product and market it under your own brand.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
The rule that applies was set by the US Supreme court long ago  and is still controlling today. It is LAWFUL to buy a branded product in bulk, repackage it, and then resell the repackaged product under the original trademark.
BUT, you must inform consumers that you’ve repackaged the product AND this rule does not apply in certain situations [when your repackaging affects the quality of the product, for example, or when the original packaging configuration is compelled by some consumer protection statute].
Read the US Supreme Court case here: Prestonettes v. Coty (permitting the repacking and sale of perfume under the original manufacturer’s trademark) (Justice Holmes): http://j.mp/dwdynf .
The key parts of that decision underlie every trademark infringement analyses: “Then what new rights does the trade mark confer? It does not confer a right to prohibit the use of the word or words. It is not a copyright. The argument drawn from the language of the Trade Mark Act does not seem to us to need discussion. A trade mark only gives the right to prohibit the use of it so far as to protect the owner's good will against the sale of another's product as his. United Drug Co. v. Theodore Rectanus Co., 248 U.S. 90, 97. … When the mark is used in a way that does not deceive the public we see no such sanctity in the word as to prevent its being used to tell the truth. It is not taboo. Canal Co. v. Clark, 13 Wall. 311, 327."
Justice Holmes was very clear when he addressed the repackaging and resale right: “If a man bought a barrel of a certain flour, or a demijohn of Old Crow whiskey, he certainly could sell the flour in smaller packages or in former days could have sold the whiskey in bottles, and tell what it was, if he stated that he did the dividing up or the bottling. And this would not be because of a license implied from the special facts but on the general ground that we have stated. It seems to us that no new right can be evoked from the fact that the perfume or powder is delicate and likely to be spoiled, or from the omnipresent possibility of fraud. If the defendant's rebottling the plaintiff's perfume deteriorates it and the public is adequately informed who does the rebottling, the public, with or without the plaintiff's assistance, is likely to find it out. And so of the powder in its new form.”
You should also read (1) Section II of the following decision for the rules that apply to repackaging and reselling branded products: Brilliance Audio, Inc., v. Haights Cross Communications at http://j.mp/9oR8u5 and (2) the entirety of a case that digs deeper into some of the exceptions to the rules: Polymer Technology Corporation v. Mimran at http://j.mp/cNdCsA .
Needless to say, you NEED to discuss your particular plans with an intellectual property attorney before you put those plans into action.