Prudy, what you don't do is consider the different constructions that you might take of those words.
"for as long as the money lasts" could be understood as an absolute gift, with any obligations being purely moral. A case where this was done is Re Lipinski's WT. It could be understood as creating only an interest in remainder with a power of appointment - that is an income only interest with a capital power of appointment - i.e. a trust of the form "Property to X, remainder to Y, X to have a power to appoint capital". A convenient way to consider these issues is under the head of certainty of intention. What the court is essentially doing in these cases is looking for the most appropriate way to analyse the facts before it - it might be a trust even if the settlor did not say "I'm creating a trust", as in Paul v Constance, or it might be something else entirely.
Don't forget the beneficiary principle. It might be possible to read these trusts as not being purpose trusts at all, but as being for the benefit of particular people. Depending on the facts, the upkeep of the grave might be seen as being for the benefit of whoever owns the graveyard. A trust for the care of the animal might be read as being for the benefit of the person who now looks after the animal rather than the animal itself. This was done in Re Denley's Trust Deed, where a sports ground was left "for the benefit of" the employees of the company. This was read as a trust granting the employees proprietary rights as beneficiaries, rather than as a abstract purpose trust - Goff J took the view that as long as the employees can take some sort of direct or indirect benefit, that is enough to make them a beneficiary.
The law regarding certainties is generally quite simple, if you have the technique they are quite easy questions. What you want to do is take each possible issue one by one (the certainties, beneficiary principle, perpetuities, formalities), consider how the facts in the question might be understood, consider the consequences of each possibility and consider which interpretation you think to be the most appropriate one on the facts.
Good luck....