There are two sections in a set of accounts that need to be signed, firstly the directors' report and secondly the balance sheet. Although a company secretary is able to sign the directors' report, only a director can sign the declaration on the balance sheet. Without the correct signatures, the accounts will be rejected. You will therefore need to make provision for your accounts to be signed before you go away, in order to avoid a late filing penalty being issued.
The corporation tax return must be signed by an 'authorised person' and this includes the company secretary. If there is not an appointed company secretary, the form must be signed by a director so again, you would need to ensure that this was dealt with before going away.
You must ensure that an original signature is used for all of the above documents, as a photocopy of a signature is not acceptable for Companies House or HM Revenue & Customs.