If I wanted to donate a few hundred euros which organisation(s) would provide the most benefits for ukrainians? Mostly thinking about humanitarian aid but I'm fine with donations to military causes as well.
The platform for donations maintained by the government of Ukraine is https://u24.gov.ua
I donate directly there, having as few middlemen as possible seems like a good idea, and you can decide on that website what your donation should be prioritized towards
Harley is a British de-mining volunteer in Ukraine, organizing, training and equipping others to find, disarm and remove mines and other UXO (unexploded ordinance)
Besides United24, there's another one organized by the Defense Ministry of Czechia called 'Gift for Putin'. It's a collection of fundraisers for... well, spicy gifts for Putin, sort to speak.
The Telegraph newspaper podcast Ukraine the Latest often profiles good ones and their stories, and I think they posted a list somewhere of recommended ones.