Your investments will remain the same when they're moved "in kind" to your account at Vanguard. An in-kind transfer is one of the quickest and easiest ways to move an account. There's no selling or buying involved, so no gain or loss is recognized as a tax consequence. Investments that can't be held at Vanguard (such as a fund that's only available at your current firm) can't be moved in kind.
After your transfer is complete, you can invest in a wide selection of products including ETFs (exchange-traded funds), mutual funds, stocks, bonds, and other securities.
If you're transferring assets from a money market fund, the shares will be liquidated and the proceeds moved as cash into your Vanguard money market settlement fund.