The most common and most likely answer to this crossword clue is the 8 letter word VIATICUM
I've seen this crossword clue in The Times
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The straight part
We know that "voyage provisions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case voyage provisions = viaticum.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does VIATICUM mean?
VIATICUM noun- The Eucharist, when given to a person who is dying or one in danger of death.
- Provisions, money, or other supplies given to someone setting off on a long journey.
- A portable altar.