There is a huge range of modern adhesive products available. Always check any product's data sheets for correct and safe use. The following table is a good guide:
1. "Araldite"-type two-part epoxy resin & hardener adhesives
2. Cyanoacrylate superglues
3. Plastic cement
4. PVA and other (waterproof) wood glues
Once again there is an enormous range of options for the modeller. For filling gaps and small holes, two-part fillers such as Milliput are useful, and for finer imperfections Squadron Putty will give an excellent finish.
To fill larger holes in the glassfibre hull (when bedding in prop shafts, bow thrusters and rudder shafts, for example) glassfibre filler is ideal, along with a 2-part resin & hardener adhesive such as Araldite.
In all circumstances, when using adhesives and fillers, proper preparation is vital. Ensure surfaces are clean and grease-free, and - if need be - keyed to provide a good contact. For adhesives, especially those used on major structural elements, clamp components together until thoroughly set.