На брелоке у меня висит второй жетон на всякий случай.

Because Russian usually does not use иметь the way English uses to have in everyday speech.

У меня висит второй жетон is literally something like At me, a second token is hanging, but naturally it means I have a second token hanging.

This pattern is very common in Russian:

• У меня есть машина = I have a car
• У меня на стене висит картина = I have a painting hanging on the wall

So here Russian combines:

• у меня = possession / “I have”
• висит = the thing is hanging

It sounds much more natural than я имею in ordinary conversation.

Because жетон is the grammatical subject of висит.

In this sentence, the thing doing the “hanging” is второй жетон:

• висит = hangs / is hanging
• второй жетон = the thing that hangs

So it stays in the nominative:

• второй жетон

If it were a direct object, you would expect another case, often accusative. But here it is the subject, so nominative is correct.

Висит is:

• 3rd person singular
• present tense
• from висеть = to hang

It is singular because the subject is singular:

• второй жетон висит = the second token is hanging

If there were several tokens, you would use the plural:

• На брелоке у меня висят два жетона.
  = I have two tokens hanging on the keychain.

Also, in Russian, the present tense of verbs like висеть often translates naturally as is hanging, not just hangs.

Because the idea is that the token is attached on the keychain, not located inside it.

• на брелоке = on the keychain / attached to the keychain
• в брелоке would suggest inside the keychain, which usually does not fit this situation

After на in a location meaning, Russian uses the prepositional case, so:

• брелок → на брелоке

Брелок usually means a keychain, key fob, or a small ornament attached to keys.

So на брелоке can mean:

• on my keychain
• on my key ring
• attached to my keys

The exact English word depends on context, but keychain is often the simplest translation for learners.

Grammatically, второй means second, but in sentences like this it often means a second one, an extra one, or a spare one.

So второй жетон here is very likely:

• a second token
• an extra token
• a spare token

It does not necessarily mean it is “token number two” in a sequence.

That is why the sentence can feel very natural in English as:

• I have a spare token on my keychain just in case. or
• I have a second token hanging on my keychain just in case.

На всякий случай is a very common fixed expression meaning:

• just in case
• for any eventuality
• to be safe

Word for word, it is something like for any case, but you should learn it as a whole idiom.

Examples:

• Возьми зонт на всякий случай.
  = Take an umbrella just in case.
• Я записал адрес на всякий случай.
  = I wrote down the address just in case.

So in your sentence, it explains why the speaker has the second token.

Yes, Russian word order is flexible, and different orders change the emphasis more than the basic meaning.

This sentence starts with На брелоке to set the scene first:

• On the keychain, I have a second token hanging...

Other possible versions:

• У меня на брелоке висит второй жетон.
• Второй жетон у меня висит на брелоке.
• На брелоке висит у меня второй жетон.
  (less neutral, more marked)

The original order sounds natural if the speaker wants to begin with the location: on the keychain.

Because на брелоке only tells you where the token is hanging.
У меня tells you whose situation this is: I have / mine.

Without у меня, the sentence would still be grammatical:

• На брелоке висит второй жетон.
  = There is a second token hanging on the keychain.

But that version does not explicitly say whose keychain or whose token it is.
Adding у меня makes the possession personal and clear.

In the present tense, Russian often omits есть.

Compare:

• У меня есть жетон. = I have a token.
• У меня на брелоке висит жетон. = I have a token hanging on my keychain.

In the second sentence, the verb висит already carries the main idea, so есть is unnecessary.

Russian usually does not stack both in a sentence like this:

• not normally у меня есть висит...

Instead, it simply uses the meaningful verb:

• висит = is hanging

Not always. Жетон can mean different things depending on context, for example:

• token
• tag
• medallion
• ID tag
• sometimes something like a subway token or cloakroom token

In this sentence, since it is hanging on a keychain, it could be some kind of tag or token attached to the keys. The exact English choice depends on what object the speaker means in real life.

So token is a safe general translation, but context may suggest something more specific.