I went through this exact mess after a trip to Zion. I tried a cheap generic cap but it fell off in my bag and almost scratched my glass.

• Sigma LCF-72 III 72mm Lens Cap: Stays put because the spring tension is way higher than cheapies.
• JJC LH-780-06 Replacement Lens Hood: Half the price of OEM but clicks in way tighter. Avoid metal tulips tho. They usually cause vignetting at 18mm because they arent optimized for the wide end.

Quick tip since you have a gig so soon. Stay away from metal hoods... they almost always vignette on wide zooms like the Sigma. Id grab a Tiffen 72mm UV Protection Filter for the glass protection instead, way safer for a busy shoot. If you need a solid cap that isnt pricey, the Sensei 72mm Center-Squeeze Lens Cap has much better springs than the absolute bottom-barrel generic ones.

Just saw this thread and had to jump in because I've gone through like five different setups for my Sigma! Honestly, the technical specs on some of these cheap accessories are just garbage and will ruin your weekend gig. I'm a bit of a nerd about build quality and after losing my original cap, I realized that mixing brands is actually the secret move here.

• The Nikon LC-72 72mm Snap-On Front Lens Cap is hands down the best. I know it's weird putting Nikon on a Sigma/Canon setup but the spring tension is insane compared to the flimsy generic ones.
• If you're worried about scratches for Saturday, the Hoya 72mm NXT Plus UV Filter is amazing for the price. It has 10 layers of HMC multicoating so you wont get that nasty ghosting in high-contrast spots.
• Seriously, avoid the metal tulips! I tried one once for the 'pro' look and the vignetting at 18mm was literally unusable. Stick to the plastic petal designs like the ProOptic 72mm Dedicated Lens Hood for Sigma 18-35mm if you want to save cash over the OEM version.

Re: "Just saw this thread and had to jump..." - honestly, I'm just here to commiserate because the struggle with the Sigma 18-35mm f/1.8 DC HSM Art accessories is just constant. I love the lens, totally satisfied with the internal focus and that wide aperture, but the cap and hood situation is a joke. Its so frustrating that we have to deal with these flimsy designs. I spent way too much time looking for a deal on a 72mm cap and every single cheap one had such weak springs that they were basically useless. It makes me so mad that the official Sigma LCF-72 III 72mm Front Lens Cap costs what it does for just being plastic, but the knockoffs are so hit or miss. I had a generic hood that literally rattled on the front of the barrel because the bayonet tolerances were so bad. Its just exhausting trying to find gear thats actually reliable without getting ripped off by the big brands...

Bump - same question here

Huh interesting. I had no idea. The more you know I guess 🤷