Learn Swedish: Du måste ta på dig haklappen före kräftskivan. - You must put on the bib before the crayfish party.

Ta på sig is a reflexive phrasal verb meaning to put on clothing. You need the reflexive pronoun (here, dig) to show you are putting it on yourself. When speaking, remember to put the emphasis on the particle på, not the verb ta.

Why use före instead of innan for before here?

Före is a preposition, meaning it must be followed by a noun phrase like kräftskivan. Innan is traditionally a conjunction used before a full clause (for example, innan kräftskivan börjar). While many native speakers casually use innan as a preposition too, före remains the standard, correct choice before a noun.

What does the skivan part of kräftskivan mean? I thought en skiva meant a slice.

You are right that en skiva normally means a slice or a disc/record. However, it also has an older meaning of a festive party or feast. Today, you will mostly only see this meaning preserved in specific compound words like kräftskiva (crayfish party) and skivmiddag (dinner party).

Could I say din haklapp (your bib) instead of just using the definite form haklappen?