You can use 'Export as Catalog', which can be found in File menu.
Basically, you select the photos you want to take with you on the trip then choose 'Export as Catalog' designating say the Pictures folder on as the destination location on your MacBook. In below screenshot I've chosen the original raw files (negatives), but easily have chosen Smart Previews instead. The advantage of these being they use much less disk space. The disadvantage being that they are only 2560 pixels on longest side and may not be ideal if you want to edit images with maximum detail.
And then when you return, use 'Import from Another Catalog' to get the images and their edits back into your main catalog.
I forgot to include a link to this tutorial Adobe Lightroom - Exporting a Catalog
Also, as Johan has mentioned, use 'Import from another catalog' to return the edits to your main catlog on the iMac. Fortunately, this is much easier than exporting as a catalog since you need only select the catalog on your MacBook.