The 'for+gerund' combination is fine. I don't really understand why Silvia changed two of them to infinitives. I'd add some prepositions, especially where it's obviously the person (as opposed to the object) which does these things: We use a chair for sitting on We use a schoolbag for keeping books in The others are OK.

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we use an eraser for rubbing words out we use a school bag TO CARRY books we use a ruler TO DRAW straight lines we use scissors for cutting things out :)