Я храню чек в кошельке на всякий случай.

I keep the receipt in my wallet just in case.

Breakdown of Я храню чек в кошельке на всякий случай.

• я: I
• в: in
• кошелёк: the wallet
• чек: the receipt

Questions & Answers about Я храню чек в кошельке на всякий случай.

Why is в кошельке (Prepositional) used instead of в кошелёк (Accusative)?

With в:

• Accusative (в кошелёк) = motion into something (putting it there): Я кладу чек в кошелёк.
• Prepositional (в кошельке) = location in something (already there): Я храню чек в кошельке.
  Here the meaning is “I keep/store it in my wallet,” so it’s location → Prepositional.

What case is чек in, and why?

Чек is Accusative singular because it’s the direct object of the verb храню (I keep): храню (что?) чек.
For an inanimate masculine noun like чек, the Accusative form looks the same as Nominative: чек.

Why does the sentence start with Я? Can it be omitted?

Yes, Я can often be omitted because the verb ending already shows the subject:

• Храню чек в кошельке на всякий случай. = “(I) keep the receipt…”
  Including Я adds emphasis/contrast (e.g., “I keep it…”).

What does храню mean exactly? Is it more like “store,” “keep,” or “save”?