Cuando se me acaba el gel, reutilizo el envase pequeño para viajar.

When I run out of gel, I reuse the small container for traveling.

Breakdown of Cuando se me acaba el gel, reutilizo el envase pequeño para viajar.

• yo: I
• pequeño: small
• cuando: when
• para: for

Questions & Answers about Cuando se me acaba el gel, reutilizo el envase pequeño para viajar.

Why is cuando followed by the present tense here?

Because this sentence describes a habitual action: something the speaker does whenever the gel runs out.

So:

• Cuando se me acaba el gel, reutilizo... = When/Whenever my gel runs out, I reuse...

In Spanish, for repeated or general situations, it is very normal to use the present tense in both parts.

Compare:

• Cuando se me acaba el gel, reutilizo el envase...
  = a usual routine
• Cuando se me acabe el gel, reutilizaré el envase...
  = one future occasion: When my gel runs out, I’ll reuse the container

So the sentence you have is about a regular habit, not a single future event.

What does se me acaba mean exactly?

Se me acaba is a very common Spanish way to say that something runs out or gets used up.

Breakdown:

• acabarse = to run out / to be finished / to get used up
• me = to me / on me
• se = part of the verb acabarse here

So se me acaba el gel is roughly:

• my gel runs out
• or more literally, the gel runs out on me

That me often shows the person affected by the situation. Spanish likes this structure a lot with things like food, money, batteries, shampoo, etc.

Examples:

• Se me acabó el café = I ran out of coffee
• Se me acaban las pilas = My batteries are running out

Why is there both se and ? Are they both necessary?