These days I tend not to travel with my Apple MacBook and instead try to do everything on my iPad. This has limitations but I've worked around most of them. However, one thing I hadn't been able to do was resize images, as even the popular Snapseed app doesn't offer this option. I've now found CropSize, which offers resizing, cropping and effects. There were no reviews at the App Store so I took a gamble and paid my £3.99.
This app is really well presented and offers great flexibility with intuitive and novel controls. There are both preset and custom resizing and cropping options, while the effects can be selected from thumbnails with each having slide of switch controls.
It's worth a try if you need to edit images on an iPad.
CropSize - Photo Resize & Crop to Exact Image Size by Khutarshchykau A