I think you are not quite right in looking for words, I would look at what interactions you expect and aim to have a word or two to make that interaction go smoother. Consider what you want them to be able to report to you; saying cat, dog, bus, car, or uncle might be helpful things for them to be able to communicate to you in a morning routine. Most interactions initiated by the adult can be worked through repeated yes/no's without too much trouble.
The words that help my interaction with a toddler most (other than the nearly impossible to avoid no, up, and family names) are in order:
- help (anything not AAAAAAHH!!!)
- please or I want
- poop (or anything similar: poo, potty, change, wet, wee)
- ouch or hurt
- here or take or this (I like New Zealand slang 'ta')
- hungry, thirsty, food, eat, drink, water (I like the ASL signs for eat and water)
- go, stop
By 3 I would expect them to understand everything. They may not be comfortable making all the sounds yet, add probably aren't practiced using big words, but they probably have work-arounds for their trouble spots, like knowing to say "like a stop sign" if someone doesn't understand their pronunciation of "red".