The first collection of Jagainu-kun 4-koma comics! First published in 1997.
Title: じゃがいぬくん
(Jagainu-kun)
ISBN：4-89309-135-2

The second collection of 4-koma comics.
Title: じゃがいぬくん2　「春だよー！」
(Jagainu-kun 2: It's spring!)
ISBN：4-89309-143-3

The third collection of 4-koma comics.
Title: じゃがいぬくん3　「ほっかほか～」
(Jagainu-kun 3: So warm~)
ISBN: 4-89309-154-9

The fourth collection of 4-koma comics.
Title: じゃがいぬくん4　「ラブラブ～?」
(Jagainu-kun 4: Love Love~?)
ISBN:4-89309-187-5

The fifth collection of 4-koma comics.
Title: じゃがいぬくん5　「ぷかぷか～」
(Jagainu-kun 5: Float along~)
ISBN: 4-89309-199-9

A black-and-white tankobon collection.
Title: もっとじゃがいぬくん
(More Jagainu-kun)
ISBN: 4-89309-199-9

The second black-and-white tankobon collection.
Title: もっともっとじゃがいぬくん
(Even More Jagainu-kun)
ISBN: 4-89309-195-6

A children's activity book.
Title: ゲームであそぼう！じゃがいぬくん
(Let's play games! Jagainu-kun)
ISBN: ISBN：4-89309-189-1

The first Jagainu-kun DVD, containing episodes 1-13.
Title: じゃがいぬくん　「しっぽは最高!」
(Jagainu-kun: The tail is the best!)

The second Jagainu-kun DVD, with episodes 24-25.
Title: じゃがいぬくん　「踊ればハッピー」
(Jagainu-kun: Dance and be happy)

A set of two Jagainu-kun hand towels, in both pink and blue!
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Scrap fabric with a Jagainu-kun design! Found on Mercari Japan.
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A Jagainu-kun plush toy. The tag is labelled Ito En, a drink company. This plush likely came out around the same time as the Ito En keychain collab!
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A soft, plush-like Jagainu-kun backpack! 25 cm x 27 cm x 4 cm.
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A set of metal keychains produced by Takara Tomy in November of 2000. They were priced at just 100 yen, including tax!!
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A set of four PVC keychains. Includes Haripoteto, Suikame, Nasuinu, and Negiwani. Unsure if this is the full collection!
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Another keychain set. The post mentions the Jagainu-kun chocolates, so maybe these came paired with boxes?
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とことこキーホルダー
A Jagainu-kun toy that walks when you wind it up! It was sold as a keychain (note the chain at the top!) Produced by SUGIYAMA & St. Works.
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A beaded keystrap. Found on second-hand website Surugaya.
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A Jagainu-kun clock! Produced by SUGIYAMA & St. Works. Found on Yahoo Auctions!

A variant of the Jagainu-kun clock above, produced by SUGIYAMA & St. Works. Found on Yahoo Auctions!

A Jagainu-kun bedside lamp! Produced by SUGIYAMA & St. Works. Found on Yahoo Auctions!

A set of iron-on adhesive name labels!

A set of iron-on patches!
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Jagainu-kun chocolate snacks! Filed under "gum and other sweets" on Mogunavi. Manufactured by Kracie Foods sometime prior to 2010.
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https://aucview.aucfan.com/yahoo/e146989363/
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A transparent plastic Jagainu-kun pencilcase!
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A Jagainu-kun CD Rom. Contains "desktop accessories." Produced by NEC Interchannel.
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A transparent plastic bento box with a 350 mL capacity.
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