Learn Hardcore Russian: Возьми с собой только нужные вещи, лишние оставь дома. - Take only the necessary things with you; leave the extra ones at home.

They are second-person singular imperatives, used to give a direct command to one person informally (the “ты” form). To address several people or to be polite/formal, use Возьмите … оставьте. You can also soften the command with words like пожалуйста or лучше.

Why use perfective imperatives (возьми, оставь) instead of бери, оставляй?

Perfective imperatives (here: взять, оставить) tell someone to do a single, complete action (pack now; leave now). Imperfective imperatives (бери, оставляй) describe repeated/habitual or ongoing actions. Compare:

One-off instruction: Возьми с собой… Лишние оставь дома.
Habitual rule: Бери с собой только нужные вещи, лишние оставляй дома.

Why is it с собой and not с тобой?

С собой uses the reflexive pronoun (instrumental case) and literally means “with yourself.” It’s the set pattern after verbs meaning “to take/bring with you”: взять/брать с собой, принести/приносить с собой.
С тобой means “with you (as a companion).” For example, Пойду с тобой = “I’ll go with you.” Also note: с “with” takes the instrumental case, hence с собой. The variant с собою is more old-fashioned/poetic.

What case is вещи in, and why do нужные and лишние look like nominative?

Вещи is the direct object of возьми, so it’s in the accusative plural. For inanimate nouns, accusative plural is the same as nominative plural, so it looks like nominative.
The adjectives нужные and лишние agree in accusative plural with an inanimate noun, so they also look like nominative plural.
In the second clause, лишние stands for лишние вещи (the noun is omitted but understood).

Why is there no noun after лишние?

It’s ellipsis: the noun вещи is omitted to avoid repetition. Russian often uses adjectives substantively when the noun is clear from context:

чёрное (платье) → чёрное
чистые (тарелки) → чистые

What does дома mean here? How is it different from в доме and домой?

дома = “at home” (location, adverbial): Он дома “He is at home.”
в доме = “in the house/building” (inside some house): Оставь вещи в доме “Leave the things in the house.”
домой = “(to) home” (motion toward): Пойду домой “I’m going home.” In the sentence, дома means “at home.”

Can I move the words around, e.g., С собой возьми только нужные вещи?

Yes. Word order is flexible for emphasis:

Возьми с собой только нужные вещи (neutral).
С собой возьми только нужные вещи (slight emphasis on taking them with you).
Только нужные вещи возьми с собой (fronts “only the necessary things” for emphasis).
Лишние оставь дома / Оставь дома лишние (both fine). Keep только right before what it limits, and keep с собой relatively close to the verb.

What’s the nuance of нужные vs необходимые, and of лишние vs запасные?

нужные = “needed/useful/necessary for your purposes” (broad, everyday).
необходимые = “indispensable/absolutely necessary” (stronger, more formal).
лишние = “extra/superfluous/redundant” (things you don’t need).
запасные = “spare/reserve” (kept as a backup), not necessarily unnecessary. You can have запасные батарейки, which aren’t лишние if you actually need spares.

How do you pronounce and stress the sentence?

Stress marks: возьми́ с собо́й то́лько ну́жные ве́щи, ли́шние оста́вь до́ма. Notes:

щ in ве́щи is pronounced like “shch.”
й in собо́й is the “y” sound in “boy.”
Stresses: возьми́, собо́й, то́лько, ну́жные, ве́щи, ли́шние, оста́вь, до́ма.

Can I replace только with лишь?

Yes. Лишь is a near-synonym, but it sounds a bit more literary/formal: Возьми с собой лишь нужные вещи, лишние оставь дома.

Can I say Возьми только нужное or Не бери лишнего?

Yes:

Возьми только нужное = “Take only what’s needed.” Here нужное is a neuter nominalized adjective (“the necessary stuff” in general).
Не бери лишнего = “Don’t take anything extra.” Лишнего is genitive singular, commonly used in this set phrase to mean “any extra (stuff).”

Why is there just a comma between the two imperatives? Could I add а?

A comma is standard to join two short, related imperatives. You can add а to emphasize contrast: Возьми с собой только нужные вещи, а лишние оставь дома. A dash is also possible stylistically, but the comma is the default.

Does взять (с собой) mean “bring” or “take”?

Взять/брать с собой covers both English “bring” and “take” depending on point of view. If you mean “bring here (to the speaker),” Russian often prefers принести/приносить; if you mean “take away (from here),” verbs like унести/увезти can be used. In packing contexts, взять с собой is the natural choice.