Lightweight app list

GTK

Terminal Emulator: st, lxterminal, sakura
Image viewer: gpicview, ristretto (xfce)
File manager: pcmanfm, thunar (xfce)
PDF Viewer: epdfview, xpdf, zathura & zathura-pdf-poppler
Archive manager: xarchiver, engrampa (mate)
Screenshot utility: flameshot, xfce-screenshooter (xfce)
Simple Text Editor: leafpad, mousepad
Text Editor: geany, textadept, cudatext, pantheon-code

Qt/Lxqt

Terminal Emulator: qterminal
Image viewer: lximage-qt
File manager: pcmanfm-qt
PDF Viewer: qpdfview
Archive manager: lxqt-archiver
Screenshot utility: screengrab (lxqt), ksnip
Text Editor: notepadqq