My google-fu is weak. It’s something like “anyone who cannot abandon their possessions at need is in fetters” but I’m not finding it.
There’s “Never own more than you can carry in both hands at a dead run.” (or sometimes seen as “You do not truly own anything that you can’t carry in both arms at a dead run.”)
There’s a bit in LoTR when Aragorn returns an elven broach to Pippin “One who cannot cast away a treasure at need is in fetters”.
But that’s Tolkien not Heinlein.
Wow. Conflating Heinlein and Tolkien. Clearly my senility has progressed further than I realized. 
I’m not finding it in The Notebooks Of Lazarus Long.
It’s in “The Door Into Summer”. I just read it. Towards the end, before he returns to the future, he meets Vikki for the last time and says something like “When your grandma shows up later today, you just tell everyone you’re going to lunch and then never come back. Don’t pack a suitcase, just go!” and Vikki says something like “But I just got a brand new bathing suit!”
Dan thinks “How do you explain to a 12(?) year old girl that you have to be prepared to abandon all your possessions from time to time?” (and then he suggests that she tell everyone that Grandma is going to take her swimming and then to lunch, but never return."
Lazarus Long (possibly in the Tale of the Adopted Daughter") makes some comment that’s similar about “A man should be prepared to abandon all his possessions at least three times in his life”.
Ricky, not Vikki, right? Short for Fredericka, I think.
P.S. Thanks for identifying where this was from.
Rikki–I knew that. (thumps head on desk) 
I found the quote online via a sketchy site that had the whole book posted (so no link), but I don’t mind saving myself some typing.
Sure there are times when you just must abandon your baggage but that’s different than it’s a good thing to do so. Heinlein certainly never practiced this.
Just because Heinlein had a character say in in one of his stories doesn’t mean he personally believed it.
Who said he personally believed it?
Heinlein wrote pro-JFK-style democracy books (Double Star), pro-dictatorship books (Glory Road), pro-anarchy/extreme libertarian books (Moon is a Harsh Mistress), etc. He wrote about many ideas that he didn’t share.
The OP was looking for a quote from a book about a specific topic. It was provided. Or were you responding to some other thread?
On a (slightly) related note, he said on at least one occasion that anyone who persisted in living on the flanks of a rumbling volcano deserved no sympathy when it erupted.
Obviously Heinlein and Tolkein both lifted the line from the seminal 1995 movie, Heat:
Don’t let yourself get attached to anything you are not willing to walk out on in 30 seconds flat if you feel the heat around the corner.
Wow so much anger when you agree with me.
He didn’t agree with you-You’re just misunderstanding things again.
Edited to add: Good pull on that quote, Fenris.
"He wrote about many ideas that he didn’t share. "
“Just because Heinlein had a character say in in one of his stories doesn’t mean he personally believed it.”
Those arent in agreement?
He just added some unnecessary snark.
“In the course of a long life, a wise man must be prepared to abandon his belongings more than once.”
Thanks. 
Nah, they all plagiarized my friend Fred: “You should be able to fit everything you own in a Honda Civic.”
The snark was in your head, but I was confused by your out-of-the-blue comment about how Heinlein may or may not have believed it.
If someone asked “I remember a poem about ghouls working in a cathedral…anyone remember it?”, and someone else answers “Poe, “The Bells””, it is not a normal response to say “Poe didn’t really believe in ghouls and didn’t think they lived in cathedrals. Just because he put it in a poem doesn’t mean he agreed with it.”
Hope this helps you understand why your response seemed so bizarre for this thread and why I thought you might have meant to reply to another thread since your comment was completely irrelevant to anything anyone had said here.