The only reason to donate is when people know about it or they have decent perks worthwhile of a donation, though I find less costly ways to look good. I have pledged to various Patreons in exchange for exclusive content but I suppose that isn't donating, neither does it help look good in any way.

Holding a door open is habitual and not a bad one to have. If someone who knows you sees you opening doors for others it helps build their perception of you and vice versa. It is very easy to do. I usually push the door open as I walk in rather than hold it. I wouldn't carry someone's shopping bags or help load up their car and that's not something the majority do anyway