Let’s say you have this long list of libraries to put into the stage-packages :

Files from the build host were migrated into the snap to satisfy dependencies that would otherwise not be met. This feature will be removed in a future release. If these libraries are needed in the final snap, ensure that the following are either satisfied by a stage-packages entry or through a part:
usr/lib/x86_64-linux-gnu/libICE.so.6
usr/lib/x86_64-linux-gnu/libSM.so.6
usr/lib/x86_64-linux-gnu/libX11-xcb.so.1
usr/lib/x86_64-linux-gnu/libX11.so.6
usr/lib/x86_64-linux-gnu/libXau.so.6
usr/lib/x86_64-linux-gnu/libXcomposite.so.1
usr/lib/x86_64-linux-gnu/libXcursor.so.1
usr/lib/x86_64-linux-gnu/libXdamage.so.1
usr/lib/x86_64-linux-gnu/libXdmcp.so.6
usr/lib/x86_64-linux-gnu/libXext.so.6
usr/lib/x86_64-linux-gnu/libXfixes.so.3
usr/lib/x86_64-linux-gnu/libXi.so.6
usr/lib/x86_64-linux-gnu/libXinerama.so.1
usr/lib/x86_64-linux-gnu/libXrandr.so.2
usr/lib/x86_64-linux-gnu/libXrender.so.1
usr/lib/x86_64-linux-gnu/libXxf86vm.so.1
usr/lib/x86_64-linux-gnu/libatk-1.0.so.0
usr/lib/x86_64-linux-gnu/libatk-bridge-2.0.so.0
usr/lib/x86_64-linux-gnu/libatspi.so.0
usr/lib/x86_64-linux-gnu/libboost_filesystem.so.1.58.0
usr/lib/x86_64-linux-gnu/libboost_system.so.1.58.0
usr/lib/x86_64-linux-gnu/libcairo-gobject.so.2
usr/lib/x86_64-linux-gnu/libcairo.so.2
usr/lib/x86_64-linux-gnu/libcapnp-0.5.3.so
usr/lib/x86_64-linux-gnu/libdatrie.so.1
usr/lib/x86_64-linux-gnu/libdrm.so.2
usr/lib/x86_64-linux-gnu/libenchant.so.1
usr/lib/x86_64-linux-gnu/libepoxy.so.0
usr/lib/x86_64-linux-gnu/libfontconfig.so.1
usr/lib/x86_64-linux-gnu/libgbm.so.1
usr/lib/x86_64-linux-gnu/libgdk-3.so.0
usr/lib/x86_64-linux-gnu/libgdk_pixbuf-2.0.so.0
usr/lib/x86_64-linux-gnu/libglapi.so.0
usr/lib/x86_64-linux-gnu/libgraphite2.so.3
usr/lib/x86_64-linux-gnu/libgstapp-1.0.so.0
usr/lib/x86_64-linux-gnu/libgstaudio-1.0.so.0
usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0
usr/lib/x86_64-linux-gnu/libgstfft-1.0.so.0
usr/lib/x86_64-linux-gnu/libgstpbutils-1.0.so.0
usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
usr/lib/x86_64-linux-gnu/libgsttag-1.0.so.0
usr/lib/x86_64-linux-gnu/libgstvideo-1.0.so.0
usr/lib/x86_64-linux-gnu/libgtk-3.so.0
usr/lib/x86_64-linux-gnu/libharfbuzz-icu.so.0
usr/lib/x86_64-linux-gnu/libharfbuzz.so.0
usr/lib/x86_64-linux-gnu/libhyphen.so.0
usr/lib/x86_64-linux-gnu/libicudata.so.55
usr/lib/x86_64-linux-gnu/libicui18n.so.55
usr/lib/x86_64-linux-gnu/libicuuc.so.55
usr/lib/x86_64-linux-gnu/libjavascriptcoregtk-4.0.so.18
usr/lib/x86_64-linux-gnu/libjbig.so.0
usr/lib/x86_64-linux-gnu/libjpeg.so.8
usr/lib/x86_64-linux-gnu/libkj-0.5.3.so
usr/lib/x86_64-linux-gnu/libmirclient.so.9
usr/lib/x86_64-linux-gnu/libmircommon.so.7
usr/lib/x86_64-linux-gnu/libmircore.so.1
usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3
usr/lib/x86_64-linux-gnu/libnotify.so.4
usr/lib/x86_64-linux-gnu/liborc-0.4.so.0
usr/lib/x86_64-linux-gnu/libpango-1.0.so.0
usr/lib/x86_64-linux-gnu/libpangocairo-1.0.so.0
usr/lib/x86_64-linux-gnu/libpangoft2-1.0.so.0
usr/lib/x86_64-linux-gnu/libpixman-1.so.0
usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.9
usr/lib/x86_64-linux-gnu/libsecret-1.so.0
usr/lib/x86_64-linux-gnu/libsoup-2.4.so.1
usr/lib/x86_64-linux-gnu/libthai.so.0
usr/lib/x86_64-linux-gnu/libtiff.so.5
usr/lib/x86_64-linux-gnu/libwayland-client.so.0
usr/lib/x86_64-linux-gnu/libwayland-cursor.so.0
usr/lib/x86_64-linux-gnu/libwayland-egl.so.1
usr/lib/x86_64-linux-gnu/libwayland-server.so.0
usr/lib/x86_64-linux-gnu/libwebkit2gtk-4.0.so.37
usr/lib/x86_64-linux-gnu/libwebp.so.5
usr/lib/x86_64-linux-gnu/libwebpdemux.so.1
usr/lib/x86_64-linux-gnu/libxcb-dri2.so.0
usr/lib/x86_64-linux-gnu/libxcb-dri3.so.0
usr/lib/x86_64-linux-gnu/libxcb-glx.so.0
usr/lib/x86_64-linux-gnu/libxcb-present.so.0
usr/lib/x86_64-linux-gnu/libxcb-render.so.0
usr/lib/x86_64-linux-gnu/libxcb-shm.so.0
usr/lib/x86_64-linux-gnu/libxcb-sync.so.1
usr/lib/x86_64-linux-gnu/libxcb-xfixes.so.0
usr/lib/x86_64-linux-gnu/libxcb.so.1
usr/lib/x86_64-linux-gnu/libxkbcommon.so.0
usr/lib/x86_64-linux-gnu/libxml2.so.2
usr/lib/x86_64-linux-gnu/libxshmfence.so.1
usr/lib/x86_64-linux-gnu/libxslt.so.1
usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1
usr/lib/x86_64-linux-gnu/mesa/libGL.so.1
Searching them one-by-one on the Ubuntu Packages Search?  Nope.
Method 1: Scripting
Copy the file list (without the prompt line) and save it as, for example, missing-libraries.txt
On the build host/container/VM’s shell, run:
 cut \
     --delimiter=':' \
     --fields=1 \
         while read -r library_file; do
             dpkg-query --search "${library_file}"
         done <missing-libraries.txt
     | env LANG=C sort \
     | uniq \
     | sed --regexp-extended 's/^(.*)$/- \1/' \
     > missing-stage-packages.yaml
Open the created missing-stage-packages.yaml file and voila!
- libatk-bridge2.0-0
- libatk1.0-0
- libatspi2.0-0
- libboost-filesystem1.58.0
- libboost-system1.58.0
- libcairo-gobject2
- libcairo2
- libcapnp-0.5.3
- libdatrie1
- libdrm2
- libegl1-mesa
- libenchant1c2a
- libepoxy0
- libfontconfig1
- libgbm1
- libgdk-pixbuf2.0-0
- libglapi-mesa
- libgraphite2-3
- libgstreamer-plugins-base1.0-0
- libgstreamer1.0-0
- libgtk-3-0
- libharfbuzz-icu0
- libharfbuzz0b
- libhyphen0
- libice6
- libicu55
- libjavascriptcoregtk-4.0-18
- libjbig0
- libjpeg-turbo8
- libmirclient9
- libmircommon7
- libmircore1
- libmirprotobuf3
- libnotify4
- liborc-0.4-0
- libpango-1.0-0
- libpangocairo-1.0-0
- libpangoft2-1.0-0
- libpixman-1-0
- libprotobuf-lite9v5
- libsecret-1-0
- libsm6
- libsoup2.4-1
- libthai0
- libtiff5
- libwayland-client0
- libwayland-cursor0
- libwayland-egl1-mesa
- libwayland-server0
- libwebkit2gtk-4.0-37
- libwebp5
- libwebpdemux1
- libx11-6
- libx11-xcb1
- libxau6
- libxcb-dri2-0
- libxcb-dri3-0
- libxcb-glx0
- libxcb-present0
- libxcb-render0
- libxcb-shm0
- libxcb-sync1
- libxcb-xfixes0
- libxcb1
- libxcomposite1
- libxcursor1
- libxdamage1
- libxdmcp6
- libxext6
- libxfixes3
- libxi6
- libxinerama1
- libxkbcommon0
- libxml2
- libxrandr2
- libxrender1
- libxshmfence1
- libxslt1.1
- libxxf86vm1
all the stage-packages entries ready to be pasted to your part’s definition.
This topic is a wiki, new tricks welcome.
          
Here is my one-liner for the task 
dpkg -S $(cat libs.txt)|sed s/:.*$//|sort|uniq|sed 's/^/ - /'
snapcraft should get a switch to do that for us