We want to get engaged without a ring or gift trays, just with a mutual agreement. Is the engagement still valid?

Yes; in the Shariah, an engagement takes place when a proposal is accepted, not because of a ring or gift trays. Rings, gift trays and ceremonies are only customs to announce and celebrate. Good customs may continue, but leaving them out takes nothing away in terms of the ruling. Announce the engagement to close relatives and write down what has been agreed so both families are clear. If any family member feels let down, explain gently: ‘We want to save for the nikah and our first home.’ Decisions made together with both families' blessing rarely cause problems. See engagement ceremony: sunnah or custom.