1. I would most likely use it like that:
—Валда, помоги Роману.
—В чём? (What exactly?) / С чем? or Чем? (With what?)/ А что случилось? (Aaand what's the problem?)

2. "Устаревший" means "obsolete". As in out-of-date technology. Food would be "с истёкшим сроком годности" (lit. "with an expired use-by date", rather formal) or just "про'сроченный"; I would recommend latter for everyday use. Note the connexion to "срок", which in this word is framed by the prefix "про-" and suffix "-ен".

3. Usually "температура", eg. "У него температура" (lit. "He's got a temperature"). Also, as an extension, it can be specified: "Дома сижу, у меня сегодня 38" ("Staying home; got 100º F today.")