I was invited to a 30th birthday a fews years back which seemed completely normal until, at the end, the couple started walking around asking for either $30 or $50 of each guest to cover costs - oh and birthday gifts were expected and accepted. In the end the birthday party was handled like a college keg party

The oddest part is this couple was very well off so it was a money grab.
Other than this bizarre event, such things are more of a regional social contract sort of thing when attending an event at a venue. This tends to depend on where this is located and the cost of the event. Up in the NYC area where events are VERY pricey cash is usually expected. By this I mean guests
should understand there is a large outlay for the event so, as a result, it is customary to "gift" cash to cover your plate at the event. So you guesstimate the cost, when at a $100 a person wedding my family would $100 in the envelope per person and gift it to the couple. Same goes for things like a Baby Shower or Bridal Shower, anything formal at a venue. If a guest can't afford it they generally stay home. There are often etiquette exceptions for very close elderly family members like grandparents who are already making a big cash outlay for a new outfit and all. Noone talks about this, it is just the way things are done.
The part with funerals could possibly be where the family of the person who died requests a donation to a charity of their choice instead of flowers. I have also seen where sometimes there is a request to help with medical expenses, funeral costs or to help pay for their kids into a college fund type thing. I suppose, if there is a diner after services or if there is a celebration of life type dinner at a restaurant the same sort of expectation to cover your plate might apply.
All of this depends on where you live. I was at a wedding in California where people wore short sets and flip-flops while dragging gifts like ironing boards to the picnic meal of ramen salad. It was a lot of fun but not something I expected or had ever seen before so the whole thing is about social norms of wherever you are.
Different strokes for different folks, as they say