Some of the main liabilities that can't be waived are liabilities arising from intentional torts, reckless conduct, willful and wanton conduct, gross negligence and bad faith. Also, often certain statutory liabilities (e.g. an obligation to pay minimum wage to employees governed by an agreement) provide on their face that they may not be waived by agreement. In the case of an insurance contract, the requirement that the insured has an insurable interest in the risk insured against can also not be waived.
Jurisdictions differ on the question of whether an overbroad waiver that purports to waive liabilities that can't be waived are completely void and must merely not be given effect with respect to liabilities that can't be waived.
But, generally speaking, claims arising as a matter of strict liability or ordinary negligence can be waived by agreement. Also, generally speaking, provisions establishing the types of damages that may be recovered and dispute resolution proceeds may be established for claims that are not or cannot be waived in advance. I say "generally speaking" because almost every general rule has at least some exceptions. For example, other limitations on warranty limitations contrary to those implied in law by the Uniform Commercial Code are provided in the Magnuson–Moss Warranty Act (P.L. 93-637) in United States (15 U.S.C. § 2301 et seq.) for consumer products.
Also, the click wrap license or agreement is only effective if adequate knowledge of its existence is available to an ordinary consumer. You can't just slip a fortune cookie fortune sized piece of paper in 4 point font that is light black against a dark black background into a big package, or an invisible text link on a webpage that doesn't show up at all on a mobile app, and expect that to be upheld in court.
And, the terms of the click wrap license have to be consistent with reasonable expectations and related to the transaction or they are void as unconscionable (e.g. you can't make a binding promise to sacrifice your dog to Loki on Samhain of 2020 merely by virtue of a click wrap agreement for tax accounting software).
A signature is not generally required, however. You can agree to a contract through actions as opposed to a signature.
UPDATE: It turns out the 2020 is so weird, that I am no longer confident that this answer is true. Check your tax software TOS! Save your dog!