Soft drink falls in Class 32, beer & soft drinks. Everything below is read from the USPTO's own list of accepted descriptions, not from an opinion about where it belongs.
Searching the USPTO Trademark ID Manual for soft drink returns 32 accepted descriptions, and all of them sit in Class 32. The manual is the list of identifications the office has already approved, so wording taken from it is pre-approved and settles the class at the same time.
The class follows from the identification you write, so "what class am I in" is really "what exactly do you sell". How the class system works covers the rest.
Beer, soft drinks, juices, seltzer, or bottled water.
32 accepted descriptions in the manual mention soft drink. For example:
Making soft drink is Class 32; a shop or online store that sells it is retail store services (Class 35), and a business that does both files in both.
Beer and non-alcoholic drinks. Wine is Class 33, so a brewery that adds a wine or a spirit is filing in a second class.
The class decides what a registration covers; it does not decide whether the name is available. Relatedness is judged on the identifications, so a conflict can sit in a class you never looked at: the same name in a different industry.
Check whether your name is clear for soft drink Searches the live USPTO register, including sound-alike and meaning-alike names. First search $2, then $5.Soft drink sits in Class 32, beer & soft drinks. That is where the USPTO's own ID Manual puts it: 32 accepted descriptions mentioning soft drink fall in Class 32.
You file in every class you actually use the mark in, and the USPTO charges its fee per class. Selling a product and also running an online store for it is two classes, not one. Filing in classes you do not use is worse than filing in too few: an application has to be supported by real use or a genuine intent to use.
No. The class decides what a registration covers. Availability turns on whether someone already holds a similar mark for related goods, and relatedness is judged on what the identifications say rather than on the class number, so marks in different classes can still conflict.
Not what you sell? Search the class finder for your own wording, or browse all 45 classes.